Standard Test Methods for Tension Testing of Metallic ... · PDF fileDesignation: E8/E8M...

Designation: E8/E8M − 13a American Association StateHighway and Transportation Officials Standard

AASHTO No.: T68An American National Standard

Standard Test Methods forTension Testing of Metallic Materials1

This standard is issued under the fixed designation E8/E8M; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the Department of Defense.

1. Scope*

1.1 These test methods cover the tension testing of metallicmaterials in any form at room temperature, specifically, themethods of determination of yield strength, yield pointelongation, tensile strength, elongation, and reduction of area.

1.2 The gauge lengths for most round specimens are re-quired to be 4D for E8 and 5D for E8M. The gauge length isthe most significant difference between E8 and E8M testspecimens. Test specimens made from powder metallurgy(P/M) materials are exempt from this requirement by industry-wide agreement to keep the pressing of the material to aspecific projected area and density.

1.3 Exceptions to the provisions of these test methods mayneed to be made in individual specifications or test methods fora particular material. For examples, see Test Methods andDefinitions A370 and Test Methods B557, and B557M.

1.4 Room temperature shall be considered to be 10 to 38°C[50 to 100°F] unless otherwise specified.

1.5 The values stated in SI units are to be regarded asseparate from inch/pound units. The values stated in eachsystem are not exact equivalents; therefore each system mustbe used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.

1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.

2. Referenced Documents

2.1 ASTM Standards:2

A356/A356M Specification for Steel Castings, Carbon, LowAlloy, and Stainless Steel, Heavy-Walled for Steam Tur-bines

A370 Test Methods and Definitions for Mechanical Testingof Steel Products

B557 Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy Products

B557M Test Methods for Tension Testing Wrought and CastAluminum- and Magnesium-Alloy Products (Metric)

E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE29 Practice for Using Significant Digits in Test Data to

Determine Conformance with SpecificationsE83 Practice for Verification and Classification of Exten-

someter SystemsE345 Test Methods of Tension Testing of Metallic FoilE691 Practice for Conducting an Interlaboratory Study to

Determine the Precision of a Test MethodE1012 Practice for Verification of Testing Frame and Speci-

men Alignment Under Tensile and Compressive AxialForce Application

D1566 Terminology Relating to RubberE1856 Guide for Evaluating Computerized Data Acquisition

Systems Used to Acquire Data from Universal TestingMachines

3. Terminology

3.1 Definitions of Terms Common to Mechanical Testing—3.1.1 The definitions of mechanical testing terms that ap-

pear in the Terminology E6 apply to this test method.1 These test methods are under the jurisdiction of ASTM Committee E28 on

Mechanical Testing and are the direct responsibility of Subcommittee E28.04 onUniaxial Testing.

Current edition approved July 1, 2013. Published August 2013. Originallyapproved in 1924. Last previous edition approved 2013 as E8/E8M – 13. DOI:10.1520/E0008_E0008M-13A.

2 For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at [email protected]. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.

*A Summary of Changes section appears at the end of this standard

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1Copyright ASTM International Provided by IHS under license with ASTM Sold to:NW PA Reg Plann and Dev Co, 811794

Not for Resale,09/25/2013 09:03:44 MDTNo reproduction or networking permitted without license from IHS

--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

3.1.1.1 These terms include bending strain, constraint,elongation, extensometer, force, gauge length, necking, re-duced section, stress-strain diagram, testing machine, andmodulus of elasticity.

3.1.2 In addition, the following common terms from Termi-nology E6 are defined:

3.1.3 discontinuous yielding, n—in a uniaxial test, a hesita-tion or fluctuation of force observed at the onset of plasticdeformation, due to localized yielding.

3.1.3.1 Discussion—The stress-strain curve need not appearto be discontinuous.

3.1.4 elongation after fracture, n—the elongation measuredby fitting the two halves of the broken specimen together.

3.1.5 elongation at fracture, n—the elongation measuredjust prior to the sudden decrease in force associated withfracture.

3.1.6 lower yield strength, LYS [FL-2]—in a uniaxial test,the minimum stress recorded during discontinuous yielding,ignoring transient effects.

3.1.7 reduction of area, n—the difference between theoriginal cross-sectional area of a tension test specimen and thearea of its smallest cross section.

3.1.7.1 Discussion—The reduction of area is usually ex-pressed as a percentage of the original cross-sectional area ofthe specimen.

3.1.7.2 Discussion—The smallest cross section may be mea-sured at or after fracture as specified for the material under test.

3.1.7.3 Discussion—The term reduction of area when ap-plied to metals generally means measurement after fracture;when applied to plastics and elastomers, measurement atfracture. Such interpretation is usually applicable to values forreduction of area reported in the literature when no furtherqualification is given. (E28.04)

3.1.8 tensile strength, Su [FL–2], n—the maximum tensilestress that a material is capable of sustaining.

3.1.8.1 Discussion—Tensile strength is calculated from themaximum force during a tension test carried to rupture and theoriginal cross-sectional area of the specimen.

3.1.9 uniform elongation, Elu, [%]—the elongation deter-mined at the maximum force sustained by the test piece justprior to necking or fracture, or both.

3.1.9.1 Discussion—Uniform elongation includes both elas-tic and plastic elongation.

3.1.10 upper yield strength, UYS [FL-2]—in a uniaxial test,the first stress maximum (stress at first zero slope) associatedwith discontinuous yielding at or near the onset of plasticdeformation.

3.1.11 yield point elongation, YPE, n—in a uniaxial test, thestrain (expressed in percent) separating the stress-strain curve’sfirst point of zero slope from the point of transition fromdiscontinuous yielding to uniform strain hardening.

3.1.11.1 Discussion— If the transition occurs over a rangeof strain, the YPE end point is the intersection between (a) ahorizontal line drawn tangent to the curve at the last zero slopeand (b) a line drawn tangent to the strain hardening portion ofthe stress-strain curve at the point of inflection. If there is no

point at or near the onset of yielding at which the slope reacheszero, the material has 0 % YPE.

3.1.12 yield strength, YS or Sy [FL–2], n—the engineeringstress at which, by convention, it is considered that plasticelongation of the material has commenced.

3.1.12.1 Discussion—This stress may be specified in termsof (a) a specified deviation from a linear stress-strainrelationship, (b) a specified total extension attained, or (c)maximum or minimum engineering stresses measured duringdiscontinuous yielding.

3.2 Definitions of Terms Specific to This Standard:3.2.1 referee test, n—test made to settle a disagreement as to

the conformance to specified requirements, or conducted by athird party to arbitrate between conflicting results. D1566,

D11.08

4. Significance and Use

4.1 Tension tests provide information on the strength andductility of materials under uniaxial tensile stresses. Thisinformation may be useful in comparisons of materials, alloydevelopment, quality control, and design under certain circum-stances.

4.2 The results of tension tests of specimens machined tostandardized dimensions from selected portions of a part ormaterial may not totally represent the strength and ductilityproperties of the entire end product or its in-service behavior indifferent environments.

4.3 These test methods are considered satisfactory for ac-ceptance testing of commercial shipments. The test methodshave been used extensively in the trade for this purpose.

5. Apparatus

5.1 Testing Machines—Machines used for tension testingshall conform to the requirements of Practices E4. The forcesused in determining tensile strength and yield strength shall bewithin the verified force application range of the testingmachine as defined in Practices E4.

5.2 Gripping Devices:5.2.1 General—Various types of gripping devices may be

used to transmit the measured force applied by the testingmachine to the test specimens. To ensure axial tensile stresswithin the gauge length, the axis of the test specimen shouldcoincide with the center line of the heads of the testingmachine. Any departure from this requirement may introducebending stresses that are not included in the usual stresscomputation (force divided by cross-sectional area).

NOTE 1—The effect of this eccentric force application may be illus-trated by calculating the bending moment and stress thus added. For astandard 12.5-mm [0.500-in.] diameter specimen, the stress increase is 1.5percentage points for each 0.025 mm [0.001 in.] of eccentricity. This errorincreases to 2.5 percentage points/ 0.025 mm [0.001 in.] for a 9 mm[0.350-in.] diameter specimen and to 3.2 percentage points/ 0.025 mm[0.001 in.] for a 6-mm [0.250-in.] diameter specimen.

NOTE 2—Alignment methods are given in Practice E1012.

5.2.2 Wedge Grips—Testing machines usually are equippedwith wedge grips. These wedge grips generally furnish asatisfactory means of gripping long specimens of ductile metal

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

and flat plate test specimens such as those shown in Fig. 1. If,however, for any reason, one grip of a pair advances fartherthan the other as the grips tighten, an undesirable bendingstress may be introduced. When liners are used behind thewedges, they must be of the same thickness and their facesmust be flat and parallel. For best results, the wedges should besupported over their entire lengths by the heads of the testingmachine. This requires that liners of several thicknesses beavailable to cover the range of specimen thickness. For propergripping, it is desirable that the entire length of the serratedface of each wedge be in contact with the specimen. Properalignment of wedge grips and liners is illustrated in Fig. 2. Forshort specimens and for specimens of many materials it isgenerally necessary to use machined test specimens and to usea special means of gripping to ensure that the specimens, whenunder load, shall be as nearly as possible in uniformlydistributed pure axial tension (see 5.2.3, 5.2.4, and 5.2.5).

5.2.3 Grips for Threaded and Shouldered Specimens andBrittle Materials—A schematic diagram of a gripping devicefor threaded-end specimens is shown in Fig. 3, while Fig. 4shows a device for gripping specimens with shouldered ends.Both of these gripping devices should be attached to the headsof the testing machine through properly lubricated spherical-seated bearings. The distance between spherical bearingsshould be as great as feasible.

5.2.4 Grips for Sheet Materials—The self-adjusting gripsshown in Fig. 5 have proven satisfactory for testing sheetmaterials that cannot be tested satisfactorily in the usual type ofwedge grips.

5.2.5 Grips for Wire—Grips of either the wedge or snubbingtypes as shown in Fig. 5 and Fig. 6 or flat wedge grips may beused.

5.3 Dimension-Measuring Devices—Micrometers and otherdevices used for measuring linear dimensions shall be accurateand precise to at least one half the smallest unit to which theindividual dimension is required to be measured.

5.4 Extensometers—Extensometers used in tension testingshall conform to the requirements of Practice E83 for theclassifications specified by the procedure section of this testmethod. Extensometers shall be used and verified to includethe strains corresponding to the yield strength and elongation atfracture (if determined).

5.4.1 Extensometers with gauge lengths equal to or shorterthan the nominal gauge length of the specimen (dimensionshown as “G-Gauge Length” in the accompanying figures) maybe used to determine the yield behavior. For specimens withouta reduced section (for example, full cross sectional areaspecimens of wire, rod, or bar), the extensometer gauge lengthfor the determination of yield behavior shall not exceed 80 %of the distance between grips. For measuring elongation atfracture with an appropriate extensometer, the gauge length ofthe extensometer shall be equal to the nominal gauge lengthrequired for the specimen being tested.

6. Test Specimens

6.1 General:

6.1.1 Specimen Size—Test specimens shall be either sub-stantially full size or machined, as prescribed in the productspecifications for the material being tested.

6.1.2 Location—Unless otherwise specified, the axis of thetest specimen shall be located within the parent material asfollows:

6.1.2.1 At the center for products 40 mm [1.500 in.] or lessin thickness, diameter, or distance between flats.

6.1.2.2 Midway from the center to the surface for productsover 40 mm [1.500 in.] in thickness, diameter, or distancebetween flats.

6.1.3 Specimen Machining—Improperly prepared test speci-mens often are the reason for unsatisfactory and incorrect testresults. It is important, therefore, that care be exercised in thepreparation of specimens, particularly in the machining, tomaximize precision and minimize bias in test results.

6.1.3.1 The reduced sections of prepared specimens shouldbe free of cold work, notches, chatter marks, grooves, gouges,burrs, rough surfaces or edges, overheating, or any othercondition which can deleteriously affect the properties to bemeasured.

NOTE 3—Punching or blanking of the reduced section may producesignificant cold work or shear burrs, or both, along the edges which shouldbe removed by machining.

6.1.3.2 Within the reduced section of rectangularspecimens, edges or corners should not be ground or abraded ina manner which could cause the actual cross-sectional area ofthe specimen to be significantly different from the calculatedarea.

6.1.3.3 For brittle materials, large radius fillets at the ends ofthe gauge length should be used.

6.1.3.4 The cross-sectional area of the specimen should besmallest at the center of the reduced section to ensure fracturewithin the gauge length. For this reason, a small taper ispermitted in the reduced section of each of the specimensdescribed in the following sections.

6.1.4 Specimen Surface Finish—When materials are testedwith surface conditions other than as manufactured, the surfacefinish of the test specimens should be as provided in theapplicable product specifications.

NOTE 4—Particular attention should be given to the uniformity andquality of surface finish of specimens for high strength and very lowductility materials since this has been shown to be a factor in thevariability of test results.

6.2 Plate-Type Specimens—The standard plate-type testspecimen is shown in Fig. 1. This specimen is used for testingmetallic materials in the form of plate, shapes, and flat materialhaving a nominal thickness of 5 mm [0.188 in.] or over. Whenproduct specifications so permit, other types of specimens maybe used, as provided in 6.3, 6.4, and 6.5.

6.3 Sheet-Type Specimens:6.3.1 The standard sheet-type test specimen is shown in Fig.

1. This specimen is used for testing metallic materials in theform of sheet, plate, flat wire, strip, band, hoop, rectangles, andshapes ranging in nominal thickness from 0.13 to 19 mm[0.005 to 0.750 in.]. When product specifications so permit,other types of specimens may be used, as provided in 6.2, 6.4,and 6.5.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

Dimensions

Standard Specimens Subsize Specimen

Plate-Type, 40 mm[1.500 in.] Wide

Sheet-Type, 12.5 mm[0.500 in.] Wide

6 mm[0.250 in.] Wide

mm [in.] mm [in.] mm [in.]

G—Gauge length (Note 1 and Note 2) 200.0 ± 0.2[8.00 ± 0.01]

50.0 ± 0.1[2.000 ± 0.005]

25.0 ± 0.1[1.000 ± 0.003]

W—Width (Note 3 and Note 4) 40.0 ± 2.0[1.500 ± 0.125, -0.250]

12.5 ± 0.2[0.500 ± 0.010]

6.0 ± 0.1[0.250 ± 0.005]

T—Thickness (Note 5) thickness of materialR—Radius of fillet, min (Note 6) 25 [1] 12.5 [0.500] 6 [0.250]L—Overall length, min (Note 2, Note 7, and Note 8) 450 [18] 200 [8] 100 [4]A—Length of reduced section, min 225 [9] 57 [2.25] 32 [1.25]B—Length of grip section, min (Note 9) 75 [3] 50 [2] 30 [1.25]C—Width of grip section, approximate (Note 4 and Note 9) 50 [2] 20 [0.750] 10 [0.375]

NOTE 1—For the 40 mm [1.500 in.] wide specimen, punch marks for measuring elongation after fracture shall be made on the flat or on the edge ofthe specimen and within the reduced section. Either a set of nine or more punch marks 25 mm [1 in.] apart, or one or more pairs of punch marks 200mm [8 in.] apart may be used.

NOTE 2—When elongation measurements of 40 mm [1.500 in.] wide specimens are not required, a minimum length of reduced section (A) of 75 mm[2.25 in.] may be used with all other dimensions similar to those of the plate-type specimen.

NOTE 3—For the three sizes of specimens, the ends of the reduced section shall not differ in width by more than 0.10, 0.05 or 0.02 mm [0.004, 0.002or 0.001 in.], respectively. Also, there may be a gradual decrease in width from the ends to the center, but the width at each end shall not be more than1 % larger than the width at the center.

NOTE 4—For each of the three sizes of specimens, narrower widths (W and C) may be used when necessary. In such cases the width of the reducedsection should be as large as the width of the material being tested permits; however, unless stated specifically, the requirements for elongation in a productspecification shall not apply when these narrower specimens are used.

NOTE 5—The dimension T is the thickness of the test specimen as provided for in the applicable material specifications. Minimum thickness of 40 mm[1.500 in.] wide specimens shall be 5 mm [0.188 in.]. Maximum thickness of 12.5 and 6 mm [0.500 and 0.250 in.] wide specimens shall be 19 and 6mm [0.750 and 0.250 in.], respectively.

NOTE 6—For the 40 mm [1.500 in.] wide specimen, a 13 mm [0.500 in.] minimum radius at the ends of the reduced section is permitted for steelspecimens under 690 MPa [100 000 psi] in tensile strength when a profile cutter is used to machine the reduced section.

NOTE 7—The dimension shown is suggested as a minimum. In determining the minimum length, the grips must not extend in to the transition sectionbetween Dimensions A and B, see Note 9.

NOTE 8—To aid in obtaining axial force application during testing of 6-mm [0.250-in.] wide specimens, the overall length should be as large as thematerial will permit, up to 200 mm [8.00 in.].

NOTE 9—It is desirable, if possible, to make the length of the grip section large enough to allow the specimen to extend into the grips a distance equalto two thirds or more of the length of the grips. If the thickness of 12.5 mm [0.500-in.] wide specimens is over 10 mm [0.375 in.], longer grips andcorrespondingly longer grip sections of the specimen may be necessary to prevent failure in the grip section.

NOTE 10—For the three sizes of specimens, the ends of the specimen shall be symmetrical in width with the center line of the reduced section within2.5, 1.25 and 0.13 mm [0.10, 0.05 and 0.005 in.], respectively. However, for referee testing and when required by product specifications, the ends of the12.5 mm [0.500 in.] wide specimen shall be symmetrical within 0.2 mm [0.01 in.].

NOTE 11—For each specimen type, the radii of all fillets shall be equal to each other within a tolerance of 1.25 mm [0.05 in.], and the centers ofcurvature of the two fillets at a particular end shall be located across from each other (on a line perpendicular to the centerline) within a tolerance of 2.5mm [0.10 in.].

NOTE 12—Specimens with sides parallel throughout their length are permitted, except for referee testing, provided: (a) the above tolerances are used;(b) an adequate number of marks are provided for determination of elongation; and (c) when yield strength is determined, a suitable extensometer is used.If the fracture occurs at a distance of less than 2 W from the edge of the gripping device, the tensile properties determined may not be representative ofthe material. In acceptance testing, if the properties meet the minimum requirements specified, no further testing is required, but if they are less than theminimum requirements, discard the test and retest.

FIG. 1 Rectangular Tension Test Specimens

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

NOTE 5—Test Methods E345 may be used for tension testing ofmaterials in thicknesses up to 0.15 mm [0.0059 in.].

6.3.2 Pin ends as shown in Fig. 7 may be used. In order toavoid buckling in tests of thin and high-strength materials, itmay be necessary to use stiffening plates at the grip ends.

6.4 Round Specimens:6.4.1 The standard 12.5-mm [0.500-in.] diameter round test

specimen shown in Fig. 8 is used quite generally for testingmetallic materials, both cast and wrought.

6.4.2 Fig. 8 also shows small-size specimens proportional tothe standard specimen. These may be used when it is necessaryto test material from which the standard specimen or specimensshown in Fig. 1 cannot be prepared. Other sizes of small round

specimens may be used. In any such small-size specimen it isimportant that the gauge length for measurement of elongation

FIG. 2 Wedge Grips with Liners for Flat Specimens

FIG. 3 Gripping Device for Threaded-End Specimens

FIG. 4 Gripping Device for Shouldered-End Specimens

FIG. 5 Gripping Devices for Sheet and Wire Specimens

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

be four times the diameter of the specimen when following E8and five times the diameter of the specimen when followingE8M.

6.4.3 The shape of the ends of the specimen outside of thegauge length shall be suitable to the material and of a shape tofit the holders or grips of the testing machine so that the forcesmay be applied axially. Fig. 9 shows specimens with varioustypes of ends that have given satisfactory results.

6.5 Specimens for Sheet, Strip, Flat Wire, and Plate—Intesting sheet, strip, flat wire, and plate, use a specimen typeappropriate for the nominal thickness of the material, asdescribed in the following:

6.5.1 For material with a nominal thickness of 0.13 to 5 mm[0.005 to 0.1875 in.], use the sheet-type specimen described in6.3.

6.5.2 For material with a nominal thickness of 5 to 12.5 mm[0.1875 to 0.500 in.], use either the sheet-type specimen of 6.3or the plate-type specimen of 6.2.

6.5.3 For material with a nominal thickness of 12.5 to 19mm [0.500 to 0.750 in.], use either the sheet-type specimen of6.3, the plate-type specimen of 6.2, or the largest practical sizeof round specimen described in 6.4.

6.5.4 For material with a nominal thickness of 19 mm[0.750 in.], or greater, use the plate-type specimen of 6.2 or thelargest practical size of round specimen described in 6.4.

6.5.4.1 If the product specifications permit, material of athickness of 19 mm [ 0.750 in.], or greater may be tested usinga modified sheet-type specimen conforming to the configura-tion shown by Fig. 1. The thickness of this modified specimenmust be machined to 10 6 0.5 mm [0.400 6 0.020 in.], andmust be uniform within 0.1 mm [0.004 in.] throughout thereduced section. In the event of disagreement, a round speci-men shall be used as the referee test (comparison) specimen.

6.6 Specimens for Wire, Rod, and Bar:6.6.1 For round wire, rod, and bar, test specimens having the

full cross-sectional area of the wire, rod, or bar shall be usedwherever practicable. The gauge length for the measurement ofelongation of wire less than 4 mm [0.125 in.] in diameter shallbe as prescribed in product specifications. When testing wire,rod, or bar having a diameter of 4 mm [0.125 in.] or larger, agauge length equal to four times the diameter shall be usedwhen following E8 and a gauge length equal to five times the

diameter shall be used when following E8M unless otherwisespecified. The total length of the specimens shall be at leastequal to the gauge length plus the length of material requiredfor the full use of the grips employed.

6.6.2 For wire of octagonal, hexagonal, or square crosssection, for rod or bar of round cross section where thespecimen required in 6.6.1 is not practicable, and for rod or barof octagonal, hexagonal, or square cross section, one of thefollowing types of specimens shall be used:

6.6.2.1 Full Cross Section (Note 6)—It is permissible toreduce the test section slightly with abrasive cloth or paper, ormachine it sufficiently to ensure fracture within the gaugemarks. For material not exceeding 5 mm [0.188 in.] in diameteror distance between flats, the cross-sectional area may bereduced to not less than 90 % of the original area withoutchanging the shape of the cross section. For material over5 mm [0.188 in.] in diameter or distance between flats, thediameter or distance between flats may be reduced by not morethan 0.25 mm [0.010 in.] without changing the shape of thecross section. Square, hexagonal, or octagonal wire or rod notexceeding 5 mm [0.188 in.] between flats may be turned to around having a cross-sectional area not smaller than 90 % ofthe area of the maximum inscribed circle. Fillets, preferablywith a radius of 10 mm [0.375 in.], but not less than 3 mm[0.125 in.], shall be used at the ends of the reduced sections.Square, hexagonal, or octagonal rod over 5 mm [0.188 in.]between flats may be turned to a round having a diameter nosmaller than 0.25 mm [0.010 in.] less than the original distancebetween flats.

NOTE 6—The ends of copper or copper alloy specimens may beflattened 10 to 50 % from the original dimension in a jig similar to thatshown in Fig. 10, to facilitate fracture within the gauge marks. Inflattening the opposite ends of the test specimen, care shall be taken toensure that the four flattened surfaces are parallel and that the two parallelsurfaces on the same side of the axis of the test specimen lie in the sameplane.

6.6.2.2 For rod and bar, the largest practical size of roundspecimen as described in 6.4 may be used in place of a testspecimen of full cross section. Unless otherwise specified inthe product specification, specimens shall be parallel to thedirection of rolling or extrusion.

6.7 Specimens for Rectangular Bar—In testing rectangularbar one of the following types of specimens shall be used:

6.7.1 Full Cross Section—It is permissible to reduce thewidth of the specimen throughout the test section with abrasivecloth or paper, or by machining sufficiently to facilitate fracturewithin the gauge marks, but in no case shall the reduced widthbe less than 90 % of the original. The edges of the midlengthof the reduced section not less than 20 mm [3⁄4 in.] in lengthshall be parallel to each other and to the longitudinal axis of thespecimen within 0.05 mm [0.002 in.]. Fillets, preferably with aradius of 10 mm [3⁄8 in.] but not less than 3 mm [1⁄8 in.] shallbe used at the ends of the reduced sections.

6.7.2 Rectangular bar of thickness small enough to fit thegrips of the testing machine but of too great width may bereduced in width by cutting to fit the grips, after which the cutsurfaces shall be machined or cut and smoothed to ensurefailure within the desired section. The reduced width shall not

FIG. 6 Snubbing Device for Testing Wire

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

be less than the original bar thickness. Also, one of the types ofspecimens described in 6.2, 6.3, and 6.4 may be used.

6.8 Shapes, Structural and Other—In testing shapes otherthan those covered by the preceding sections, one of the typesof specimens described in 6.2, 6.3, and 6.4 shall be used.

6.9 Specimens for Pipe and Tube (Note 7):6.9.1 For all small tube (Note 7), particularly sizes 25 mm

[1 in.] and under in nominal outside diameter, and frequentlyfor larger sizes, except as limited by the testing equipment, it isstandard practice to use tension test specimens of full-sizetubular sections. Snug-fitting metal plugs shall be inserted farenough into the ends of such tubular specimens to permit thetesting machine jaws to grip the specimens properly. The plugsshall not extend into that part of the specimen on which theelongation is measured. Elongation is measured over a lengthof four times the diameter when following E8 or five times thediameter when following E8M unless otherwise stated in theproduct specification. Fig. 11 shows a suitable form of plug, thelocation of the plugs in the specimen, and the location of thespecimen in the grips of the testing machine.

NOTE 7—The term “tube” is used to indicate tubular products ingeneral, and includes pipe, tube, and tubing.

6.9.2 For large-diameter tube that cannot be tested in fullsection, longitudinal tension test specimens shall be cut asindicated in Fig. 12. Specimens from welded tube shall belocated approximately 90° from the weld. If the tube-wallthickness is under 20 mm [0.750 in.], either a specimen of theform and dimensions shown in Fig. 13 or one of the small-size

specimens proportional to the standard 12.5-mm [0.500-in.]specimen, as mentioned in 6.4.2 and shown in Fig. 8, shall beused. Specimens of the type shown in Fig. 13 may be testedwith grips having a surface contour corresponding to thecurvature of the tube. When grips with curved faces are notavailable, the ends of the specimens may be flattened withoutheating. If the tube-wall thickness is 20 mm [0.750 in.] or over,the standard specimen shown in Fig. 8 shall be used.

NOTE 8—In clamping of specimens from pipe and tube (as may be doneduring machining) or in flattening specimen ends (for gripping), care mustbe taken so as not to subject the reduced section to any deformation orcold work, as this would alter the mechanical properties.

6.9.3 Transverse tension test specimens for tube may betaken from rings cut from the ends of the tube as shown in Fig.14. Flattening of the specimen may be either after separating asin A, or before separating as in B. Transverse tension testspecimens for large tube under 20 mm [0.750 in.] in wallthickness shall be either of the small-size specimens shown inFig. 8 or of the form and dimensions shown for Specimen 2 inFig. 13. When using the latter specimen, either or both surfacesof the specimen may be machined to secure a uniformthickness, provided not more than 15 % of the normal wallthickness is removed from each surface. For large tube 20 mm[0.750 in.] and over in wall thickness, the standard specimenshown in Fig. 8 shall be used for transverse tension tests.Specimens for transverse tension tests on large welded tube todetermine the strength of welds shall be located perpendicularto the welded seams, with the welds at about the middle of theirlengths.

Dimensions, mm [in.]

G—Gauge length 50.0 ± 0.1 [2.000 ± 0.005]W—Width (Note 1) 12.5 ± 0.2 [0.500 ± 0.010]T—Thickness, max (Note 2) 16 [0.625]R—Radius of fillet, min (Note 3) 13 [0.5]L—Overall length, min 200 [8]A—Length of reduced section, min 57 [2.25]B—Length of grip section, min 50 [2]C—Width of grip section, approximate 50 [2]D—Diameter of hole for pin, min (Note 4) 13 [0.5]E—Edge distance from pin, approximate 40 [1.5]F—Distance from hole to fillet, min 13 [0.5]

NOTE 1—The ends of the reduced section shall differ in width by not more than 0.1 mm [0.002 in.]. There may be a gradual taper in width from theends to the center, but the width at each end shall be not more than 1 % greater than the width at the center.

NOTE 2—The dimension T is the thickness of the test specimen as stated in the applicable product specifications.NOTE 3—For some materials, a fillet radius R larger than 13 mm [0.500 in.] may be needed.NOTE 4—Holes must be on center line of reduced section within 6 0.05mm [0.002 in].NOTE 5—Variations of dimensions C, D, E, F, and L may be used that will permit failure within the gauge length.

FIG. 7 Pin-Loaded Tension Test Specimen with 50-mm [2-in.] Gauge Length

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

Dimensions, mm [in.]For Test Specimens with Gauge Length Four times the Diameter [E8]

StandardSpecimen

Small-Size Specimens Proportional to Standard

Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5

G—Gauge length 50.0 ± 0.1[2.000 ± 0.005]

36.0 ± 0.1[1.400 ± 0.005]

24.0 ± 0.1[1.000 ± 0.005]

16.0 ± 0.1[0.640 ± 0.005]

10.0 ±0.1[0.450 ± 0.005]

D—Diameter (Note 1) 12.5 ± 0.2[0.500 ± 0.010]

9.0 ±0.1[0.350 ± 0.007]

6.0 ± 0.1[0.250 ± 0.005]

4.0 ± 0.1[0.160 ± 0.003]

2.5 ± 0.1[0.113 ± 0.002]

R—Radius of fillet, min 10 [0.375] 8 [0.25] 6 [0.188] 4 [0.156] 2 [0.094]A—Length of reduced section, min (Note 2) 56 [2.25] 45 [1.75] 30 [1.25] 20 [0.75] 16 [0.625]

Dimensions, mm [in.]For Test Specimens with Gauge Length Five times the Diameter [E8M]

Standard Specimen Small-Size Specimens Proportional to StandardSpecimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5

G—Gauge length 62.5 ± 0.1[2.500 ± 0.005]

45.0 ± 0.1[1.750 ± 0.005]

30.0 ± 0.1[1.250 ± 0.005]

20.0 ± 0.1[0.800 ± 0.005]

12.5 ± 0.1[0.565 ± 0.005]

D—Diameter (Note 1) 12.5 ± 0.2[0.500 ± 0.010]

9.0 ± 0.1[0.350 ± 0.007]

6.0 ± 0.1[0.250 ± 0.005]

4.0 ± 0.1[0.160 ± 0.003]

2.5 ± 0.1[0.113 ± 0.002]

R—Radius of fillet, min 10 [0.375] 8 [0.25] 6 [0.188] 4 [0.156] 2 [0.094]A—Length of reduced section, min (Note 2) 75 [3.0] 54 [2.0] 36 [1.4] 24 [1.0] 20 [0.75]

NOTE 1—The reduced section may have a gradual taper from the ends toward the center, with the ends not more than 1 % larger in diameter than thecenter (controlling dimension).

NOTE 2—If desired, the length of the reduced section may be increased to accommodate an extensometer of any convenient gauge length. Referencemarks for the measurement of elongation should, nevertheless, be spaced at the indicated gauge length.

NOTE 3—The gauge length and fillets may be as shown, but the ends may be of any form to fit the holders of the testing machine in such a way thatthe force shall be axial (see Fig. 9). If the ends are to be held in wedge grips it is desirable, if possible, to make the length of the grip section great enoughto allow the specimen to extend into the grips a distance equal to two thirds or more of the length of the grips.

NOTE 4—On the round specimens in Figs. 8 and 9, the gauge lengths are equal to four [E8] or five times [E8M] the nominal diameter. In some productspecifications other specimens may be provided for, but unless the 4-to-1 [E8] or 5-to-1 [E8M] ratio is maintained within dimensional tolerances, theelongation values may not be comparable with those obtained from the standard test specimen.

NOTE 5—The use of specimens smaller than 6-mm [0.250-in.] diameter shall be restricted to cases when the material to be tested is of insufficient sizeto obtain larger specimens or when all parties agree to their use for acceptance testing. Smaller specimens require suitable equipment and greater skillin both machining and testing.

NOTE 6—For inch/pound units only: Five sizes of specimens often used have diameters of approximately 0.505, 0.357, 0.252, 0.160, and 0.113 in.,the reason being to permit easy calculations of stress from loads, since the corresponding cross-sectional areas are equal or close to 0.200, 0.100, 0.0500,0.0200, and 0.0100 in.2, respectively. Thus, when the actual diameters agree with these values, the stresses (or strengths) may be computed using thesimple multiplying factors 5, 10, 20, 50, and 100, respectively. (The metric equivalents of these five diameters do not result in correspondingly convenientcross-sectional areas and multiplying factors.)

FIG. 8 Standard 12.5-mm [0.500-in.] Round Tension Test Specimen and Examples of Small-Size SpecimensProportional to the Standard Specimen

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

Dimensions, mm [in.]For Test Specimens with Gauge Length Four times the Diameter [E8]

Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5

G—Gauge length 50 ± 0.1[2.000 ± 0.005]

50 ± 0.1[2.000 ± 0.005]

50 ± 0.1[2.000 ± 0.005]

50 ± 0.1[2.000 ± 0.005]

50 ± 0.1[2.000 ± 0.005]

D—Diameter (Note 1) 12.5 ± 0.2[0.500 ± 0.010]

12.5 ± 0.2[0.500 ± 0.010]

12.5 ± 0.2[0.500 ± 0.010]

12.5 ± 0.2[0.500 ± 0.010]

12.5 ± 0.2[0.500 ± 0.010]

R—Radius of fillet, min 10 [0.375] 10 [0.375] 2 [0.0625] 10 [0.375] 10 [0.375]A—Length of reduced section 56 [2.25]

min56 [2.25]

min100 [4]

approximate56 [2.25]

min56 [2.25]

minL—Overall length, approximate 145 [5] 155 [5.5] 155 [5.5] 140 [4.75] 255 [9.5]B—Length of end section (Note 3) 35 [1.375]

approximate25 [1]


approximate15 [0.5]

approximate75 [3]min

C—Diameter of end section 20 [0.75] 20 [0.75] 20 [0.75] 22 [0.875] 20 [0.75]E—Length of shoulder and fillet section, approximate 15 [0.625] 20 [0.75] 15 [0.625]F—Diameter of shoulder 15 [0.625] 15 [0.625] 15 [0.625]

Dimensions, mm [in.]For Test Specimens with Gauge Length Five times the Diameter [E8M]

Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5G—Gauge length 62.5 ± 0.1

[2.500 ± 0.005]62.5 ± 0.1

[2.500 ± 0.005]62.5 ± 0.1

[2.500 ± 0.005]62.5 ± 0.1

[2.500 ± 0.005]62.5 ± 0.1

[2.500 ± 0.005]D—Diameter (Note 1) 12.5 ± 0.2

[0.500 ± 0.010]12.5 ± 0.2

[0.500 ± 0.010]12.5 ± 0.2

[0.500 ± 0.010]12.5 ± 0.2

[0.500 ± 0.010]12.5 ± 0.2

[0.500 ± 0.010]R—Radius of fillet, min 10 [0.375] 10 [0.375] 2 [0.0625] 10 [0.375] 10 [0.375]A—Length of reduced section 75 [3]

min75 [3]min

75 [3]approximate

75 [3]min

75 [3]min

L—Overall length, approximate 145 [5] 155 [5.5] 155 [5.5] 140 [4.75] 255 [9.5]B—Length of end section (Note 3) 35 [1.375]

approximate25 [1]


approximate15 [0.5]

approximate75 [3]min

C—Diameter of end section 20 [0.75] 20 [0.75] 20 [0.75] 22 [0.875] 20 [0.75]E—Length of shoulder and fillet section, approximate 15 [0.625] 20 [0.75] 15 [0.625]F—Diameter of shoulder 15 [0.625] 15 [0.625] 15 [0.625]

NOTE 1—The reduced section may have a gradual taper from the ends toward the center with the ends not more than 1 %. larger in diameter than thecenter.

NOTE 2—On Specimens 1 and 2, any standard thread is permissible that provides for proper alignment and aids in assuring that the specimen will breakwithin the reduced section.

NOTE 3—On Specimen 5 it is desirable, if possible, to make the length of the grip section great enough to allow the specimen to extend into the gripsa distance equal to two thirds or more of the length of the grips.

NOTE 4—The values stated in SI units in the table for Fig. 9 are to be regarded as separate from the inch/pound units. The values stated in each systemare not exact equivalents; therefore each system must be used independently of the other.

FIG. 9 Various Types of Ends for Standard Round Tension Test Specimens

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

6.10 Specimens for Forgings—For testing forgings, thelargest round specimen described in 6.4 shall be used. If roundspecimens are not feasible, then the largest specimen describedin 6.5 shall be used.

6.10.1 For forgings, specimens shall be taken as provided inthe applicable product specifications, either from the predomi-nant or thickest part of the forging from which a coupon can be

obtained, or from a prolongation of the forging, or fromseparately forged coupons representative of the forging. Whennot otherwise specified, the axis of the specimen shall beparallel to the direction of grain flow.

6.11 Specimens for Castings—In testing castings either thestandard specimen shown in Fig. 8 or the specimen shown inFig. 15 shall be used unless otherwise provided in the productspecifications.

6.11.1 Test coupons for castings shall be made as shown inFig. 16 and Table 1.

6.12 Specimen for Malleable Iron—For testing malleableiron the test specimen shown in Fig. 17 shall be used, unlessotherwise provided in the product specifications.

6.13 Specimen for Die Castings—For testing die castingsthe test specimen shown in Fig. 18 shall be used unlessotherwise provided in the product specifications.

6.14 Specimens for Powder Metallurgy (P/M) Materials—For testing powder metallurgy (P/M) materials the test speci-mens shown in Figs. 19 and 20 shall be used, unless otherwiseprovided in the product specifications. When making testspecimens in accordance with Fig. 19, shallow transversegrooves, or ridges, may be pressed in the ends to allowgripping by jaws machined to fit the grooves or ridges. Becauseof shape and other factors, the flat unmachined tensile testspecimen (Fig. 19) in the heat treated condition will have anultimate tensile strength of 50 % to 85 % of that determined ina machined round tensile test specimen (Fig. 20) of likecomposition and processing.

7. Procedures

7.1 Preparation of the Test Machine—Upon startup, orfollowing a prolonged period of machine inactivity, the testmachine should be exercised or warmed up to normal operatingtemperatures to minimize errors that may result from transientconditions.

7.2 Measurement of Dimensions of Test Specimens:7.2.1 To determine the cross-sectional area of a test

specimen, measure the dimensions of the cross section at thecenter of the reduced section. For referee testing of specimensless than 5 mm [0.188 in.] in their least dimension, measure thedimensions where the least cross-sectional area is found.Measure and record the cross-sectional dimensions of tensiontest specimens as follows:

(1) Specimen dimension ≥ 5 mm [0.200 in.] to the nearest0.02 mm [0.001 in.].

(2) 2.5 mm [0.100 in.] ≤ Specimen dimension < 5 mm[0.200 in.] to the nearest 0.01 mm [0.0005 in.].

(3) 0.5 mm [0.020 in.] ≤ specimen dimension < 2.5 mm[0.100 in.] to the nearest 0.002 mm [0.0001 in.].

(4) Specimen dimensions < 0.5 mm [0.020 in.], to at leastthe nearest 1 % when practical but in all cases to at least thenearest 0.002 mm [0.0001 in.].

NOTE 9—Accurate and precise measurement of specimen dimensionscan be one of the most critical aspects of tension testing, depending onspecimen geometry. See Appendix X2 for additional information.

NOTE 10—Rough surfaces due to the manufacturing process such as hotrolling, metallic coating, etc., may lead to inaccuracy of the computed

FIG. 10 Squeezing Jig for Flattening Ends of Full-Size TensionTest Specimens

NOTE 1—The diameter of the plug shall have a slight taper from the linelimiting the test machine jaws to the curved section.

FIG. 11 Metal Plugs for Testing Tubular Specimens, Proper Loca-tion of Plugs in Specimen and of Specimen in Heads of Testing

Machine

NOTE 1—The edges of the blank for the specimen shall be cut parallelto each other.

FIG. 12 Location from Which Longitudinal Tension Test Speci-mens Are to be Cut from Large-Diameter Tube

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

areas greater than the measured dimensions would indicate. Therefore,cross-sectional dimensions of test specimens with rough surfaces due toprocessing may be measured and recorded to the nearest 0.02 mm [0.001in.]

NOTE 11—See X2.9 for cautionary information on measurements takenfrom coated metal products.

7.2.2 Determine the cross-sectional area of a full-size testspecimen of uniform but nonsymmetrical cross section bydetermining the mass of a length not less than 20 times longerthan the largest cross-sectional dimension.

7.2.2.1 Determine the weight to the nearest 0.5 % or less.

7.2.2.2 The cross-sectional area is equal to the mass of thespecimen divided by the length and divided by the density ofthe material.

7.2.3 When using specimens of the type shown in Fig. 13taken from tubes, the cross-sectional area shall be determinedas follows:

If D/W ≤ 6:

Dimensions

Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5 Specimen 6 Specimen 7

mm [in.] mm [in.] mm [in.] mm [in.] mm [in.] mm [in.] mm [in.]

G—Gauge length 50.0 ± 0.1[2.000 ± 0.005]

50.0 ± 0.1[2.000 ± 0.005]

200.0 ± 0.2[8.00 ± 0.01]

50.0 ± 0.1[2.000 ± 0.005]

100.0 ± 0.1[4.000 ± 0.005]

50.0 ± 0.1[2.000 ± 0.005]

100.0 ± 0.1[4.000 ± 0.005]

W—Width (Note 1) 12.5 ± 0.2[0.500 ± 0.010]

40.0 ± 2.0[1.5 ± 0.125-0.25]

40.0 ± 0.2[1.5 ± 0.125,-0.25]

20.0 ± 0.7[0.750 ± 0.031]

20.0 ± 0.7[0.750 ± 0.031]

25.0 ± 1.5[1.000 ± 0.062]

25.0 ± 1.5[1.000 ± 0.062]

T—Thickness measured thickness of specimenR—Radius of fillet, min 12.5 [0.5] 25 [1] 25 [1] 25 [1] 25 [1] 25 [1] 25 [1]A—Length of reducedsection,

min

60 [2.25] 60 [2.25] 230 [9] 60 [2.25] 120 [4.5] 60 [2.25] 120 [4.5]

B—Length of grip section,min (Note 2)

75 [3] 75 [3] 75 [3] 75 [3] 75 [3] 75 [3] 75 [3]

C—Width of grip section,approximate (Note 3)

20 [0.75] 50 [2] 50 [2] 25 [1] 25 [1] 40 [1.5] 40 [1.5]

NOTE 1—The ends of the reduced section shall differ from each other in width by not more than 0.5 %. There may be a gradual taper in width fromthe ends to the center, but the width at each end shall be not more than 1 % greater than the width at the center.

NOTE 2—It is desirable, if possible, to make the length of the grip section great enough to allow the specimen to extend into the grips a distance equalto two thirds or more of the length of the grips.

NOTE 3—The ends of the specimen shall be symmetrical with the center line of the reduced section within 1 mm [0.05 in.] for specimens 1, 4, and5, and 2.5 mm [0.10 in.] for specimens 2, 3, 6, and 7.

NOTE 4—For each specimen type, the radii of all fillets shall be equal to each other within a tolerance of 1.25 mm [ 0.05 in.], and the centers of curvatureof the two fillets at a particular end shall be located across from each other (on a line perpendicular to the centerline) within a tolerance of 2.5 mm [0.10in.].

NOTE 5—For circular segments, the cross-sectional area may be calculated by multiplying W and T. If the ratio of the dimension W to the diameterof the tubular section is larger than about 1⁄6, the error in using this method to calculate the cross-sectional area may be appreciable. In this case, the exactequation (see 7.2.3) must be used to determine the area.

NOTE 6—Specimens with G/W less than 4 should not be used for determination of elongation.NOTE 7—Specimens with sides parallel throughout their length are permitted, except for referee testing, provided: (a) the above tolerances are used;

(b) an adequate number of marks are provided for determination of elongation; and (c) when yield strength is determined, a suitable extensometer is used.If the fracture occurs at a distance of less than 2 W from the edge of the gripping device, the tensile properties determined may not be representative ofthe material. If the properties meet the minimum requirements specified, no further testing is required, but if they are less than the minimum requirements,discard the test and retest.

FIG. 13 Tension Test Specimens for Large-Diameter Tubular Products

FIG. 14 Location of Transverse Tension Test Specimen in RingCut from Tubular Products

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

A 5 F S W4 D 3=~D2 2 W2!G1F S D2

4 D 3 arcsinS WD D G 2 F S W

4 D3=~D 2 2T!2 2 W2G 2 F S D 2 2T

2 D 2

3 arcsinS WD 2 2T D G (1)

where:A = exact cross-sectional area, mm2 [in.2],W = width of the specimen in the reduced section, mm [in.],D = measured outside diameter of the tube, mm [in.], andT = measured wall thickness of the specimen, mm [in.].

arcsin values to be in radiansIf D/W > 6, the exact equation or the following equation maybe used:

A 5 W 3 T (2)

where:A = approximate cross-sectional area, mm2 [in.2],W = width of the specimen in the reduced section, mm [in.],

andT = measured wall thickness of the specimen, mm [in.].

NOTE 12—See X2.8 for cautionary information on measurements andcalculations for specimens taken from large-diameter tubing.

7.3 Gauge Length Marking of Test Specimens:7.3.1 The gauge length for the determination of elongation

shall be in accordance with the product specifications for the

material being tested. Gauge marks shall be stamped lightlywith a punch, scribed lightly with dividers or drawn with ink aspreferred. For material that is sensitive to the effect of slightnotches and for small specimens, the use of layout ink will aidin locating the original gauge marks after fracture.

7.3.2 For materials where the specified elongation is 3 % orless, measure the original gauge length to the nearest 0.05 mm[0.002 in.] prior to testing.

7.4 Zeroing of the Testing Machine:7.4.1 The testing machine shall be set up in such a manner

that zero force indication signifies a state of zero force on thespecimen. Any force (or preload) imparted by the gripping ofthe specimen (see Note 13) must be indicated by the forcemeasuring system unless the preload is physically removedprior to testing. Artificial methods of removing the preload onthe specimen, such as taring it out by a zero adjust pot orremoving it mathematically by software, are prohibited be-cause these would affect the accuracy of the test results.

NOTE 13—Preloads generated by gripping of specimens may be eithertensile or compressive in nature and may be the result of such things as:

— grip design— malfunction of gripping apparatus (sticking, binding, etc.)— excessive gripping force— sensitivity of the control loopNOTE 14—It is the operator’s responsibility to verify that an observed

preload is acceptable and to ensure that grips operate in a smooth manner.Unless otherwise specified, it is recommended that momentary (dynamic)forces due to gripping not exceed 20 % of the material’s nominal yieldstrength and that static preloads not exceed 10 % of the material’s nominalyield strength.

7.5 Gripping of the Test Specimen:7.5.1 For specimens with reduced sections, gripping of the

specimen shall be restricted to the grip section, becausegripping in the reduced section or in the fillet can significantlyaffect test results.

7.6 Speed of Testing:7.6.1 Speed of testing may be defined in terms of (a) rate of

straining of the specimen, (b) rate of stressing of the specimen,(c) crosshead speed, (d) the elapsed time for completing part orall of the test, or (e) free-running crosshead speed (rate ofmovement of the crosshead of the testing machine when notunder load).

7.6.2 Specifying suitable numerical limits for speed andselection of the method are the responsibilities of the productcommittees. Suitable limits for speed of testing should bespecified for materials for which the differences resulting fromthe use of different speeds are of such magnitude that the testresults are unsatisfactory for determining the acceptability ofthe material. In such instances, depending upon the materialand the use for which the test results are intended, one or moreof the methods described in the following paragraphs isrecommended for specifying speed of testing.

NOTE 15—Speed of testing can affect test values because of the ratesensitivity of materials and the temperature-time effects.

7.6.2.1 Rate of Straining—The allowable limits for rate ofstraining shall be specified in mm/mm/min [in./in./min]. Sometesting machines are equipped with pacing or indicatingdevices for the measurement and control of rate of straining,

Dimensions

Specimen 1 Specimen 2 Specimen 3

mm [in.] mm [in.] mm [in.]

G—Length of parallelsection

Shall be equal to or greater than diameter D

D—Diameter 12.5 ± 0.2[0.500 ± 0.010]

20 ± 0.4[0.750 ± 0.015]

36.0 ± 0.6[1.25 ± 0.02]

R—Radius of fillet,min

25 [1] 25 [1] 50 [2]

A—Length of reducedsection,

min

32 [1.25] 38 [1.5] 60 [2.25]

L—Overall length, min 95 [3.75] 100 [4] 160 [6.375]B—Length of endsection,

approximate

25 [1] 25 [1] 45 [1.75]

C—Diameter of endsection,

approximate

20 [0.75] 30 [1.125] 48 [1.875]

E—Length of shoulder,min

6 [0.25] 6 [0.25] 8 [0.312]

F—Diameter of shoul-der

16.0 ± 0.4[0.625 ± 0.016]

24.0 ± 0.4[0.94 ± 0.016]

36.5 ± 0.4[1.438 ± 0.016]

NOTE 1—The reduced section and shoulders (dimensions A, D, E, F, G,and R) shall be as shown, but the ends may be of any form to fit the holdersof the testing machine in such a way that the force can be axial.Commonly the ends are threaded and have the dimensions B and C givenabove.

FIG. 15 Standard Tension Test Specimen for Cast Iron

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

but in the absence of such a device the average rate of strainingcan be determined with a timing device by observing the timerequired to effect a known increment of strain.

7.6.2.2 Rate of Stressing—The allowable limits for rate ofstressing shall be specified in megapascals per second [poundsper square inch per minute]. Many testing machines areequipped with pacing or indicating devices for the measure-ment and control of the rate of stressing, but in the absence ofsuch a device the average rate of stressing can be determinedwith a timing device by observing the time required to apply aknown increment of stress.

7.6.2.3 Crosshead Speed—The allowable limits for cross-head speed, during a test, may be specified in mm/min[in./min]; in this case, the limits for the crosshead speed shouldbe further qualified by specifying different limits for varioustypes and sizes of specimens. In cases where different lengthspecimens may be used, it is often more practical to specify thecrosshead speed in terms of mm [in.] per mm [in.] of length ofthe original reduced section of the specimen (or distancebetween grips for specimens not having reduced sections) perminute. Many testing machines are equipped with pacing orindicating devices for the measurement and control of thecrosshead speed during a test, but in the absence of suchdevices the average crosshead speed can be experimentallydetermined by using suitable length-measuring and timingdevices.

NOTE 16—This method of specifying speed of testing, “CrossheadSpeed”, was previously called “Rate of Separation of Heads DuringTests.”

NOTE 17—For machines not having crossheads or having stationary

crossheads, the phrase “crosshead speed” may be interpreted to mean therate of grip separation.

7.6.2.4 Elapsed Time—The allowable limits for the elapsedtime from the beginning of force application (or from somespecified stress) to the instant of fracture, to the maximumforce, or to some other stated stress, shall be specified inminutes or seconds. The elapsed time can be determined witha timing device.

7.6.2.5 Free-Running Crosshead Speed—The allowablelimits for the rate of movement of the crosshead of the testingmachine, with no force applied by the testing machine, shall bespecified in mm per mm [inches per inch] of length of reducedsection (or distance between grips for specimens not havingreduced sections) per second [minute]. The limits for thecrosshead speed may be further qualified by specifying differ-ent limits for various types and sizes of specimens. The averagecrosshead speed can be experimentally determined by usingsuitable length-measuring and timing devices.

NOTE 18—For machines not having crossheads or having stationarycrossheads, the phrase “free-running crosshead speed” may be interpretedto mean the free-running rate of grip separation.

7.6.3 Speed of Testing When Determining Yield Properties—Unless otherwise specified, any convenient speed of testingmay be used up to one half the specified minimum yieldstrength or up to one quarter of the specified minimum tensilestrength, whichever is smaller. The speed above this point shallbe within the specified limits. If different speed limitations arerequired for use in determining yield strength, yield pointelongation, tensile strength, elongation, and reduction of area,

TABLE 1 Details of Test Coupon Design for Castings (see Fig. 16)

NOTE 1—Test Coupons for Large and Heavy Steel Castings: The test coupons in Fig. 16A and B are to be used for large and heavy steel castings.However, at the option of the foundry the cross-sectional area and length of the standard coupon may be increased as desired. This provision does notapply to Specification A356/A356M.

NOTE 2—Bend Bar: If a bend bar is required, an alternate design (as shown by dotted lines in Fig. 16) is indicated.

Leg Design, 125 mm [5 in.] Riser Design

1. L (length) A 125mm [5-in.] minimum length will be used.This length may be increased at the option of thefoundry to accommodate additional test bars (seeNote 1).

1. L (length) The length of the riser at the base will be thesame as the top length of the leg. The length ofthe riser at the top therefore depends on theamount of taper added to the riser.

2. End taperUse of and size of end taper is at the option ofthe foundry.

2. Width

The width of the riser at the base of a multiple-legcoupon shall be n (57 mm) – 16 mm [n (2.25 in.)– 0.625 in.] where n equals the number of legsattached to the coupon. The width of the riser atthe top is therefore dependent on the amount oftaper added to the riser.

3. Height 32 mm [1.25 in.]4. Width (at top) 32 mm [1.25 in.] (see Note 1)5. Radius (at bottom) 13 mm [0.5 in.] max6. Spacing between legs A 13 mm [0.5 in.] radius will be used between the

legs.7. Location of test bars The tensile, bend, and impact bars will be taken

from the lower portion of the leg (see Note 2).

8. Number of legsThe number of legs attached to the coupon is atthe option of the foundry providing they areequispaced according to Item 6.

3. T (riser taper)Height

Use of and size is at the option of the foundry.The minimum height of the riser shall be 51 mm[2 in.]. The maximum height is at the option of thefoundry for the following reasons: (a) many risersare cast open, (b) different compositions may re-quire variation in risering for soundness, or (c)different pouring temperatures may require varia-tion in risering for soundness.

9. Rx Radius from 0 to approximately 2 mm [0.062 in.]

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

FIG. 16 Test Coupons for Castings

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

they should be stated in the product specifications. In all cases,the speed of testing shall be such that the forces and strainsused in obtaining the test results are accurately indicated.Determination of mechanical properties for comparison ofproduct properties against a specification value should be runusing the same control method and rate used to determine thespecification value unless it can be shown that another methodyields equivalent or conservative results. In the absence of anyspecified limitations, one of the following control methodsshall be used. Appendix X4 provides additional guidance onselecting the control method.

NOTE 19—In the previous and following paragraphs, the yield proper-ties referred to include yield strength, yield point, and yield pointelongation.

7.6.3.1 Control Method A—Rate of Stressing Method forDetermining Yield Properties - In this method, the testingmachine shall be operated such that the rate of stress applica-tion in the linear elastic region is between 1.15 and 11.5 MPa/s[10 000 and 100 000 psi/min]. The speed of the testing machineshall not be increased in order to maintain a stressing rate whenthe specimen begins to yield. It is not recommended that the

testing machine be operated in closed-loop control using theforce signal through yield; however closed-loop control of theforce signal can be used in the linear-elastic portion of the test.

NOTE 20—It is not the intent of this method to maintain constant stressrate or to control stress rate with closed loop force control whiledetermining yield properties, but only to set the crosshead speed toachieve the target stress rate in the elastic region. When a specimen beingtested begins to yield, the stressing rate decreases and may even becomenegative in the case of a specimen with discontinuous yielding. Tomaintain a constant stressing rate through the yielding process requires thetesting machine to operate at extremely high speeds and, in most cases,this is neither practical nor desirable. In practice, it is simpler to use eithera strain rate, crosshead speed, or a free-running crosshead speed thatapproximates the desired stressing rate in the linear-elastic portion of thetest. As an example, use a strain rate that is between 1.15 and 11.5 MPa/sdivided by the nominal Young’s Modulus of the material being tested. Asanother example, find a crosshead speed through experimentation thatapproximates the desired stressing rate prior to the onset of yielding, andmaintain that crosshead speed through the region that yield properties aredetermined. While both of these methods will provide similar rates ofstressing and straining prior to the onset of yielding, the rates of stressingand straining are generally quite different in the region where yieldproperties are determined.

NOTE 21—This method has been the default method for many years for


D—Diameter 16 [0.625]R—Radius of fillet 8 [0.312]A—Length of reduced section 64 [2.5]L—Overall length 190 [7.5]B—Length of end section 64 [2.5]C—Diameter of end section 20 [0.75]E—Length of fillet 5 [0.188]

FIG. 17 Standard Tension Test Specimen for Malleable Iron


G—Gauge length 50 ± 0.1 [2.000 ± 0.005]D—Diameter (see Note) 6.4 ± 0.1 [0.250 ± 0.005]R—Radius of fillet, min 75 [3]A—Length of reduced section, min 60 [2.25]L—Overall length, min 230 [9]B—Distance between grips, min 115 [4.5]C—Diameter of end section, approximate 10 [0.375]

NOTE 1—The reduced section may have a gradual taper from the end toward the center, with the ends not more than 0.1 mm [0.005 in.] larger indiameter than the center.

FIG. 18 Standard Tension Test Specimens for Die Castings

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

testing materials that exhibit low strain rate sensitivity such as some steelsand aluminum.

7.6.3.2 Control Method B - Rate of Straining ControlMethod for Determining Yield Properties—In this method, thetesting machine shall be operated in closed-loop control usingthe extensometer signal. The rate of straining shall be set andmaintained at 0.015 6 0.006 mm/mm/min [in./in./min].

NOTE 22—Proper precautions must be observed when operating amachine in closed-loop strain control because unexpected crossheadmovement may occur if the control parameters are not set properly, ifproper safety limits are not set, or if the extensometer slips.

NOTE 23—A Rate of Straining at 0.005 mm/mm/min [in./in./min] isoften required for aerospace, high-temperature alloys, and titaniumapplications and when specified, must be followed rather than therequirement above.

7.6.3.3 Control Method C—-Crosshead Speed ControlMethod for Determining Yield Properties–The testing machineshall be set to a crosshead speed equal to 0.015 6 0.003mm/mm/min [in./in./min] of the original reduced section(dimension A in Fig. 1, Fig. 7, Fig. 8, Fig. 9, Fig. 13, Fig. 15,Fig. 17, Fig. 18, and Fig. 20, and 2 times dimension A in Fig.19) or distance between grips for specimens without reducedsections.

NOTE 24—It is recommended that crosshead speed be used for controlin regions of discontinuous yielding.

NOTE 25—Using different Control Methods may produce different yieldresults especially if the material being tested is strain-rate sensitive. Toachieve the best reproducibility in cases where the material may bestrain-rate sensitive, the same control method should be used. Methodsdescribed in 7.6.3.2 or 7.6.3.3 will tend to give similar results in the caseof a strain-rate sensitive material. The control method described in 7.6.3.1should be avoided for strain rate sensitive materials if it is desirable toreproduce similar test results on other testing machines or in otherlaboratories.

7.6.4 Speed of Testing When Determining TensileStrength—In the absence of any specified limitations on speed

of testing, the following general rules shall apply for materialswith expected elongations greater than 5 %. When determiningonly the tensile strength, or after the yield behavior has beenrecorded, the speed of the testing machine shall be set between0.05 and 0.5 mm/mm [or in./in.] of the length of the reducedsection (or distance between the grips for specimens not havinga reduced section) per minute. Alternatively, an extensometerand strain rate indicator may be used to set the strain ratebetween 0.05 and 0.5 mm/mm/min [or in./in./min].

NOTE 26—For materials with expected elongations less than or equal to5 %, the speed of the testing machine may be maintained throughout thetest at the speed used to determine yield properties.

NOTE 27—Tensile strength and elongation are sensitive to test speed formany materials (see Appendix X1) to the extent that variations within therange of test speeds given above can significantly affect results.

7.7 Determination of Yield Strength—Determine yieldstrength by any of the methods described in 7.7.1 to 7.7.4.

Pressing Area = 645 mm2 [1.00 in.2]


G—Gauge length 25.4 ± 0.08 [1.000 ± 0.003]D—Width at center 5.72 ± 0.03 [0.225 ± 0.001]W—Width at end of reducedsection

5.97 ± 0.03 [0.235 ± 0.001]

T—Compact to this thickness 3.56 to 6.35 [0.140 to 0.250]R—Radius of fillet 25.4 [1]A—Half-length of reduced sec-tion

15.9 [0.625]

B—Grip length 80.95 ± 0.03 [3.187 ± 0.001]L—Overall length 89.64 ± 0.03 [3.529 ± 0.001]C—Width of grip section 8.71 ± 0.03 [0.343 ± 0.001]F—Half-width of grip section 4.34 ± 0.03 [0.171 ± 0.001]E—End radius 4.34 ± 0.03 [0.171 ± 0.001]

NOTE 1—Dimensions Specified, except G and T, are those of the die.FIG. 19 Standard Flat Unmachined Tension Test Specimens for

Powder Metallurgy (P/M) Products

Approximate Pressing Area of Unmachined Compact = 752 mm2

[1.166 in.2] Machining Recommendations1. Rough machine reduced section to 6.35-mm [0.25-in.] diameter2. Finish turn 4.75/4.85-mm [0.187/0.191-in.] diameter with radii and

taper3. Polish with 00 emery cloth4. Lap with crocus cloth


G—Gauge length 25.4 ± 0.08 [1.000 ± 0.003]D—Diameter at center of reducedsection

4.75 ± 0.03 [0.187± 0.001]

H—Diameter at ends of gauge length 4.85 ± 0.03 [0.191 ± 0.001]R—Radius of gauge fillet 6.35 ± 0.13 [0.250 ± 0.005]A—Length of reduced section 47.63 ± 0.13 [1.875 ± 0.003]L—Overall length (die cavity length) 75 [3], nominalB—Length of end section 7.88 ± 0.13 [0.310 ± 0.005]C—Compact to this end thickness 10.03 ± 0.13 [0.395 ± 0.005]W—Die cavity width 10.03 ± 0.08 [0.395 ± 0.003]E—Length of shoulder 6.35 ± 0.13 [0.250 ± 0.005]F—Diameter of shoulder 7.88 ± 0.03 [0.310 ± 0.001]J—End fillet radius 1.27 ± 0.13 [0.050 ± 0.005]

NOTE 1—The gauge length and fillets of the specimen shall be asshown. The ends as shown are designed to provide a practical minimumpressing area. Other end designs are acceptable, and in some cases arerequired for high-strength sintered materials.

NOTE 2—It is recommended that the test specimen be gripped with asplit collet and supported under the shoulders. The radius of the colletsupport circular edge is to be not less than the end fillet radius of the testspecimen.

NOTE 3—Diameters D and H are to be concentric within 0.03 mm[0.001 in.] total indicator runout (T.I.R.), and free of scratches and toolmarks.

FIG. 20 Standard Round Machined Tension Test Specimen forPowder Metallurgy (P/M) Products

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

Where extensometers are employed, use only those that areverified over a strain range in which the yield strength will bedetermined (see 5.4).

NOTE 28—For example, a verified strain range of 0.2 % to 2.0 % isappropriate for use in determining the yield strengths of many metals.

NOTE 29—Determination of yield behavior on materials which cannotsupport an appropriate extensometer (thin wire, for example) is problem-atic and outside the scope of this standard.

7.7.1 Offset Method—To determine the yield strength by theoffset method, it is necessary to secure data (autographic ornumerical) from which a stress-strain diagram may be drawn.Then on the stress-strain diagram (Fig. 21) lay off Om equal tothe specified value of the offset, draw mn parallel to OA, andthus locate r, the intersection of mn with the stress-straindiagram (Note 36). In reporting values of yield strengthobtained by this method, the specified value of offset usedshould be stated in parentheses after the term yield strength.Thus:

Yield strength ~offset 5 0.2 %! 5 360 MPa @52 000 psi# (3)

In using this method, a Class B2 or better extensometer (seePractice E83) shall be used.

NOTE 30—There are two general types of extensometers, averaging andnon-averaging, the use of which is dependent on the product tested. Formost machined specimens, there are minimal differences. However, forsome forgings and tube sections, significant differences in measured yieldstrength can occur. For these cases, it is recommended that the averagingtype be used.

NOTE 31—When there is a disagreement over yield properties, the offsetmethod for determining yield strength is recommended as the referee testmethod.

NOTE 32—In practice, for a number of reasons, the straight-line portionof the stress-strain curve (line OA shown in Fig. 21) may not go throughthe origin of the stress-strain diagram. In these cases, Point O in Figs.21-27is not the origin of the stress-strain diagram, but rather where thestraight-line portion of the stress-strain curve, OA, intersects the strainaxis, see Fig. 26 and Fig. 27. All offsets and extensions are calculated fromthe intersection of the straight-line portion of the stress-strain curve, OA,with the strain axis, and not necessarily from the origin of the stress-straindiagram.

7.7.2 Extension-Under-Load (EUL) Method—Yield strengthby the extension-under-load method may be determined by: (1)using autographic or numerical devices to secure stress-straindata, and then analyzing this data (graphically or usingautomated methods) to determine the stress value at thespecified value of extension, or (2) using devices that indicatewhen the specified extension occurs, so that the stress thenoccurring may be ascertained (Note 34). Any of these devicesmay be automatic. This method is illustrated in Fig. 22. Thestress at the specified extension shall be reported as follows:

Yield strength ~EUL 5 0.5 %! 5 52 000 psi (4)

Extensometers and other devices used in determination ofthe extension shall meet or exceed Class B2 requirements (seePractice E83) at the strain of interest, except where use oflow-magnification Class C devices is helpful, such as in

Strain

Stress

YS(offset = 0m %)

A n

r

0 m

0m = specified offset

FIG. 21 Stress-Strain Diagram for Determination of YieldStrength by the Offset Method

Strain

Stress

YS(EUL = 0m %)

n

r

0 m

0m = specified extension under load

FIG. 22 Stress-Strain Diagram for Determination of YieldStrength by the Extension-Under-Load Method

Strain

Stress

UYS

FIG. 23 Stress-Strain Diagram Showing Upper Yield StrengthCorresponding with Top of Knee

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

facilitating measurement of YPE, if observed. If Class Cdevices are used, this must be reported along with the results.

NOTE 33—The appropriate value of the total extension must bespecified. For steels with nominal yield strengths of less than 550 MPa[80 000 psi], an appropriate value is 0.005 mm/mm [or in./in.] (0.5 %) ofthe gauge length. For higher strength steels, a greater extension or theoffset method should be used.

NOTE 34—When no other means of measuring elongation are available,a pair of dividers or similar device can be used to determine a point ofdetectable elongation between two gauge marks on the specimen. Thegauge length shall be 50 mm [2 in.]. The stress corresponding to the loadat the instant of detectable elongation may be recorded as the approximateextension-under-load yield strength.

7.7.3 Autographic Diagram Method (for materials exhibit-ing discontinuous yielding)—Obtain stress-strain (or force-elongation) data or construct a stress-strain (or force-elongation) diagram using an autographic device. Determinethe upper or lower yield strength as follows:

7.7.3.1 Record the stress corresponding to the maximumforce at the onset of discontinuous yielding as the upper yieldstrength. This is illustrated in Figs. 23 and 24.

NOTE 35—If multiple peaks are observed at the onset of discontinuousyielding, the first is considered the upper yield strength. (See Fig. 24.)

7.7.3.2 Record the minimum stress observed during discon-tinuous yielding (ignoring transient effects) as the lower yieldstrength. This is illustrated in Fig. 24.

NOTE 36—Yield properties of materials exhibiting yield point elonga-tion are often less repeatable and less reproducible than those of similarmaterials having no YPE. Offset and EUL yield strengths may besignificantly affected by stress fluctuations occurring in the region wherethe offset or extension intersects the stress-strain curve. Determination ofupper or lower yield strengths (or both) may therefore be preferable forsuch materials, although these properties are dependent on variables such

Strain

Stress

UYS

t

t

t-t : tangent to strain hardening at point of inflectionh-h : horizontal tangent at the last zero slope

h hLYS

YPE

FIG. 24 Stress-Strain Diagram Showing Yield Point Elongation(YPE) and Upper (UYS) and Lower (LYS) Yield Strengths

Strain

Stress

Inflection

FIG. 25 Stress-Strain Diagram With an Inflection, But No YPE

Elongation

Force

Fmax

0

Elu

FIG. 26 Stress-Strain Diagram in Which the Upper Yield Strengthis the Maximum Stress Recorded Method

Elongation

Force

Maximumforce

0

Elu

plateau region

Elongation

Force

Maximumforce, Fmax 0.5% Fmax

Detail of plateau region(force scale magnified)

Elu

0

FIG. 27 Force-Elongation Diagram for Determination of UniformElongation of Steel Sheet Materials Exhibiting a Plateau at Maxi-

mum Force

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

as test machine stiffness and alignment. Speed of testing may also have asignificant effect, regardless of the method employed.

NOTE 37—Where low-magnification autographic recordings are neededto facilitate measurement of yield point elongation for materials whichmay exhibit discontinuous yielding, Class C extensometers may beemployed. When this is done but the material exhibits no discontinuousyielding, the extension-under-load yield strength may be determinedinstead, using the autographic recording (see Extension-Under-LoadMethod).

7.7.4 Halt-of-the-Force Method (for materials exhibitingdiscontinuous yielding)—Apply an increasing force to thespecimen at a uniform deformation rate. When the forcehesitates, record the corresponding stress as the upper yieldstrength.

NOTE 38—The Halt-of-the-Force Method was formerly known as theHalt-of-the-Pointer Method, the Drop-of-the-Beam Method, and theHalt-of-the-Load Method.

7.8 Yield Point Elongation—Calculate the yield point elon-gation from the stress-strain diagram or data by determiningthe difference in strain between the upper yield strength (firstzero slope) and the onset of uniform strain hardening (seedefinition of YPE in Terminology E6 and Fig. 24).

NOTE 39—The stress-strain curve of a material exhibiting only a hint ofthe behavior causing YPE may have an inflection at the onset of yieldingwith no point where the slope reaches zero (Fig. 25). Such a material hasno YPE, but may be characterized as exhibiting an inflection. Materialsexhibiting inflections, like those with measurable YPE, may in certainapplications acquire an unacceptable surface appearance during forming.

7.9 Uniform Elongation (if required):7.9.1 Uniform elongation shall include both plastic and

elastic elongation.7.9.2 Uniform elongation shall be determined using auto-

graphic methods with extensometers conforming to PracticeE83. Use a class B2 or better extensometer for materials havinga uniform elongation less than 5 %. Use a class C or betterextensometer for materials having a uniform elongation greaterthan or equal to 5 % but less than 50 %. Use a class D or betterextensometer for materials having a uniform elongation of50 % or greater.

7.9.3 Determine the uniform elongation as the elongation atthe point of maximum force from the force elongation datacollected during a test.

7.9.3.1 Some materials exhibit a yield point followed byconsiderable elongation where the yield point is the maximumforce achieved during the test. In this case, uniform elongationis not determined at the yield point, but instead at the highestforce occurring just prior to necking (see Fig. 26).

7.9.3.2 Stress-strain curves for some materials exhibit alengthy, plateau-like region in the vicinity of the maximumforce. For such materials, determine the uniform elongation atthe center of the plateau as indicated in Fig. 27 (see also Note40 below).

NOTE 40—When uniform elongation is being determined digitally,noise in the stress-strain data generally causes many small, local peaks andvalleys to be recorded in the plateau region. To accommodate this, thefollowing procedure is recommended:

— Determine the maximum force recorded (after discontinuous yield-ing).

— Evaluate the sequence of force values recorded before and after themaximum force.

— Digitally define the “plateau” as consisting of all consecutive datapoints wherein the force value is within 0.5 % of the magnitude of thepeak force value.

— Determine the uniform elongation as the strain at the mid-point ofthe “plateau.”

7.9.3.3 Discussion—The 0.5 % value of Note 40 has beenselected arbitrarily. In actual practice, the value should beselected so as to be the minimum figure that is large enough toeffectively define the force plateau. This may require that thepercentage be about five times the amplitude of the forcefluctuations occurring due to noise. Values ranging from 0.1 %to 1.0 % may be found to work acceptably.

7.10 Tensile Strength (also known as Ultimate TensileStrength)—Calculate the tensile strength by dividing the maxi-mum force carried by the specimen during the tension test bythe original cross-sectional area of the specimen.

NOTE 41—If the upper yield strength is the maximum stress recorded,and if the stress-strain curve resembles that of Fig. 26, it is recommendedthat the maximum stress after discontinuous yielding be reported as thetensile strength. Where this may occur, determination of the tensilestrength should be in accordance with the agreement between the partiesinvolved.

7.11 Elongation:

7.11.1 In reporting values of elongation, give both theoriginal gauge length and the percentage increase. If anydevice other than an extensometer is placed in contact with thespecimen’s reduced section during the test, this also shall benoted.

Example: Elongation 5 30 % increase ~50 2 mm @2

2 in.# gauge length! (5)

NOTE 42—Elongation results are very sensitive to variables such as: (a)speed of testing, (b) specimen geometry (gauge length, diameter, width,and thickness), (c) heat dissipation (through grips, extensometers, or otherdevices in contact with the reduced section), (d) surface finish in reducedsection (especially burrs or notches), (e) alignment, and (f) fillets andtapers. Parties involved in comparison or conformance testing shouldstandardize the above items, and it is recommended that use of ancillarydevices (such as extensometer supports) which may remove heat fromspecimens be avoided. See Appendix X1 for additional information on theeffects of these variables.

7.11.2 When the specified elongation is greater than 3 %, fitends of the fractured specimen together carefully and measurethe distance between the gage marks to the nearest 0.25 mm[0.01 in.] for gauge lengths of 50 mm [2 in.] and under, and toat least the nearest 0.5 % of the gauge length for gauge lengthsover 50 mm [2 in.]. A percentage scale reading to 0.5 % of thegauge length may be used.

7.11.3 When the specified elongation is 3 % or less, deter-mine the elongation of the specimen using the followingprocedure, except that the procedure given in 7.11.2 may beused instead when the measured elongation is greater than 3 %.

7.11.3.1 Prior to testing, measure the original gauge lengthof the specimen to the nearest 0.05 mm [0.002 in.].

7.11.3.2 Remove partly torn fragments that will interferewith fitting together the ends of the fractured specimen or withmaking the final measurement.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

7.11.3.3 Fit the fractured ends together with matched sur-faces and apply a force along the axis of the specimen sufficientto close the fractured ends together. If desired, this force maythen be removed carefully, provided the specimen remainsintact.

NOTE 43—The use of a force generating a stress of approximately15 MPa [2000 psi] has been found to give satisfactory results on testspecimens of aluminum alloy.

7.11.3.4 Measure the final gauge length to the nearest0.05 mm [0.002 in.] and report the elongation to the nearest0.2 %.

7.11.4 Elongation measured per paragraph 7.11.2 or 7.11.3may be affected by location of the fracture, relative to themarked gauge length. If any part of the fracture occurs outsidethe gauge marks or is located less than 25 % of the elongatedgauge length from either gauge mark, the elongation valueobtained using that pair of gauge marks may be abnormallylow and non-representative of the material. If such an elonga-tion measure is obtained in acceptance testing involving only aminimum requirement and meets the requirement, no furthertesting need be done. Otherwise, discard the test and retest thematerial.

7.11.5 Elongation at Fracture:7.11.5.1 Elongation at fracture shall include elastic and

plastic elongation and may be determined with autographic orautomated methods using extensometers verified over thestrain range of interest (see 5.4). Use a class B2 or betterextensometer for materials having less than 5 % elongation, aclass C or better extensometer for materials having elongationgreater than or equal to 5 % but less than 50 %, and a class Dor better extensometer for materials having 50 % or greaterelongation. In all cases, the extensometer gauge length shall bethe nominal gauge length required for the specimen beingtested. Due to the lack of precision in fitting fractured endstogether, the elongation after fracture using the manual meth-ods of the preceding paragraphs may differ from the elongationat fracture determined with extensometers.

7.11.5.2 Percent elongation at fracture may be calculateddirectly from elongation at fracture data and be reportedinstead of percent elongation as calculated in 7.11.2 to 7.11.3.However, these two parameters are not interchangeable. Use ofthe elongation at fracture method generally provides morerepeatable results.

NOTE 44—When disagreements arise over the percent elongationresults, agreement must be reached on which method to use to obtain theresults.

7.12 Reduction of Area:7.12.1 The reduced area used to calculate reduction of area

(see 7.11.2 and 7.11.3) shall be the minimum cross section atthe location of fracture.

7.12.2 Specimens with Originally Circular Cross Sections—Fit the ends of the fractured specimen together and measure thereduced diameter to the same accuracy as the original mea-surement.

NOTE 45—Because of anisotropy, circular cross sections often do notremain circular during straining in tension. The shape is usually elliptical,thus, the area may be calculated by π · d1·d2/4, where d1 and d2 are themajor and minor diameters, respectively.

7.12.3 Specimens with Original Rectangular CrossSections—Fit the ends of the fractured specimen together andmeasure the thickness and width at the minimum cross sectionto the same accuracy as the original measurements.

NOTE 46—Because of the constraint to deformation that occurs at thecorners of rectangular specimens, the dimensions at the center of theoriginal flat surfaces are less than those at the corners. The shapes of thesesurfaces are often assumed to be parabolic. When this assumption is made,an effective thickness, te, may be calculated as follows: (t1 + 4t2 + t3)/6,where t1 and t3 are the thicknesses at the corners, and t2 is the thicknessat mid-width. An effective width may be similarly calculated.

7.12.4 Calculate the reduced area based upon the dimen-sions determined in 7.12.2 or 7.12.3. The difference betweenthe area thus found and the area of the original cross sectionexpressed as a percentage of the original area is the reductionof area.

7.12.5 If any part of the fracture takes place outside themiddle half of the reduced section or in a punched or scribedgauge mark within the reduced section, the reduction of areavalue obtained may not be representative of the material. Inacceptance testing, if the reduction of area so calculated meetsthe minimum requirements specified, no further testing isrequired, but if the reduction of area is less than the minimumrequirements, discard the test results and retest.

7.12.6 Results of measurements of reduction of area shall berounded using the procedures of Practice E29 and any specificprocedures in the product specifications. In the absence of aspecified procedure, it is recommended that reduction of areatest values in the range from 0 to 10 % be rounded to thenearest 0.5 % and test values of 10 % and greater to the nearest1 %.

7.13 Rounding Reported Test Data for Yield Strength andTensile Strength—Test data should be rounded using theprocedures of Practice E29 and the specific procedures in theproduct specifications. In the absence of a specified procedurefor rounding the test data, one of the procedures described inthe following paragraphs is recommended.

7.13.1 For test values up to 500 MPa [50 000 psi], round tothe nearest 1 MPa [100 psi]; for test values of 500 MPa[50 000 psi] and up to 1000 MPa [100 000 psi], round to thenearest 5 MPa [500 psi]; for test values of 1000 MPa [100 000psi] and greater, round to the nearest 10 MPa [1000 psi].

NOTE 47—For steel products, see Test Methods and Definitions A370.

7.13.2 For all test values, round to the nearest 1 MPa[100 psi].

NOTE 48—For aluminum- and magnesium-alloy products, see MethodsB557.

7.13.3 For all test values, round to the nearest 5 MPa[500 psi].

7.14 Replacement of Specimens—A test specimen may bediscarded and a replacement specimen selected from the samelot of material in the following cases:

7.14.1 The original specimen had a poorly machinedsurface,

7.14.2 The original specimen had the wrong dimensions,7.14.3 The specimen’s properties were changed because of

poor machining practice,

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

7.14.4 The test procedure was incorrect,7.14.5 The fracture was outside the gauge length,7.14.6 For elongation determinations, the fracture was out-

side the middle half of the gauge length, or7.14.7 There was a malfunction of the testing equipment.

NOTE 49—The tension specimen is inappropriate for assessing sometypes of imperfections in a material. Other methods and specimensemploying ultrasonics, dye penetrants, radiography, etc., may be consid-ered when flaws such as cracks, flakes, porosity, etc., are revealed duringa test and soundness is a condition of acceptance.

8. Report

8.1 Test information on materials not covered by a productspecification should be reported in accordance with 8.2 or both8.2 and 8.3.

8.2 Test information to be reported shall include the follow-ing when applicable:

8.2.1 Reference to the standard used, i.e. E8 or E8M.8.2.2 Material and sample identification.8.2.3 Specimen type (see Section 6).8.2.4 Yield strength and the method used to determine yield

strength (see 7.7).8.2.5 Yield point elongation (see 7.8).8.2.6 Tensile Strength (also known as Ultimate Tensile

Strength) (see 7.10).8.2.7 Elongation (report original gauge length, percentage

increase, and method used to determine elongation; i.e. atfracture or after fracture) (see 7.11).

8.2.8 Uniform Elongation, if required (see 7.9).8.2.9 Reduction of area, if required (see 7.12).

8.3 Test information to be available on request shall include:8.3.1 Specimen test section dimension(s).8.3.2 Equation used to calculate cross-sectional area of

rectangular specimens taken from large-diameter tubular prod-ucts.

8.3.3 Speed and method used to determine speed of testing(see 7.6).

8.3.4 Method used for rounding of test results (see 7.13).8.3.5 Reasons for replacement specimens (see 7.14).

9. Precision and Bias

9.1 Precision—An interlaboratory test program3 gave thefollowing values for coefficients of variation for the mostcommonly measured tensile properties:

Coefficient of Variation, %

TensileStrength

YieldStrength

Offset= 0.02 %

YieldStrength

Offset= 0.2 %

ElongationGaugeLength

= 4Diameter

Reductionof

AreaCV %r

CV %R

0.91.3

2.74.5

1.42.3

2.85.4

2.84.6

CV %r = repeatability coefficient of variation in percent within a laboratoryCV %R = repeatability coefficient of variation in percent betweenlaboratories

9.1.1 The values shown are the averages from tests on sixfrequently tested metals, selected to include most of the normalrange for each property listed above. When these materials arecompared, a large difference in coefficient of variation is found.Therefore, the values above should not be used to judgewhether the difference between duplicate tests of a specificmaterial is larger than expected. The values are provided toallow potential users of this test method to assess, in generalterms, its usefulness for a proposed application.

9.2 Bias—The procedures in Test Methods E8/E8M formeasuring tensile properties have no bias because these prop-erties can be defined only in terms of a test method.

10. Keywords

10.1 accuracy; bending stress; discontinuous yielding; drop-of-the-beam; eccentric force application; elastic extension;elongation; extension-under-load; extensometer; force; free-running crosshead speed; gauge length; halt-of-the force;percent elongation; plastic extension; preload; rate of stressing;rate of straining; reduced section; reduction of area; sensitivity;strain; stress; taring; tensile strength; tension testing; yieldpoint elongation; yield strength

APPENDIXES

(Nonmandatory Information)

X1. FACTORS AFFECTING TENSION TEST RESULTS

X1.1 The precision and bias of tension test strength andductility measurements depend on strict adherence to the statedtest procedure and are influenced by instrumental and materialfactors, specimen preparation, and measurement/testing errors.

X1.2 The consistency of agreement for repeated tests of thesame material is dependent on the homogeneity of the material,and the repeatability of specimen preparation, test conditions,and measurements of the tension test parameters.

X1.3 Instrumental factors that can affect test results include:the stiffness, damping capacity, natural frequency, and mass ofmoving parts of the tensile test machine; accuracy of forceindication and use of forces within the verified range of themachine; rate of force application, alignment of the testspecimen with the applied force, parallelness of the grips, grippressure, nature of the force control used, appropriateness andcalibration of extensometers, heat dissipation (by grips,extensometers, or ancillary devices), and so forth.

3 Supporting data can be found in Appendix X1 and additional data are availablefrom ASTM Headquarters. Request RR:E28-1004.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

X1.4 Material factors that can affect test results include:representativeness and homogeneity of the test material, sam-pling scheme, and specimen preparation (surface finish, dimen-sional accuracy, fillets at the ends of the gauge length, taper inthe gauge length, bent specimens, thread quality, and so forth).

X1.4.1 Some materials are very sensitive to the quality ofthe surface finish of the test specimen (see Note 4) and must beground to a fine finish, or polished to obtain correct results.

X1.4.2 Test results for specimens with as-cast, as-rolled,as-forged, or other non-machined surface conditions can beaffected by the nature of the surface (see Note 10).

X1.4.3 Test specimens taken from appendages to the part orcomponent, such as prolongs or risers, or from separatelyproduced castings (for example, keel blocks) may produce testresults that are not representative of the part or component.

X1.4.4 Test specimen dimensions can influence test results.For cylindrical or rectangular specimens, changing the testspecimen size generally has a negligible effect on the yield andtensile strength but may influence the upper yield strength, ifone is present, and elongation and reduction of area values.Comparison of elongation values determined using differentspecimens requires that the following ratio be controlled:

Lo/~Ao!1/2 (X1.1)

where:Lo = original gauge length of specimen, andAo = original cross-sectional area of specimen.

X1.4.4.1 Specimens with smaller Lo/(Ao)1/2 ratios generallygive greater elongation and reduction in area values. This is thecase for example, when the width or thickness of a rectangulartensile test specimen is increased.

X1.4.4.2 Holding the Lo/(Ao)1/2 ratio constant minimizes,but does not necessarily eliminate, differences. Depending onmaterial and test conditions, increasing the size of the propor-tional specimen of Fig. 8 may be found to increase or decreaseelongation and reduction in area values somewhat.

X1.4.5 Use of a taper in the gauge length, up to the allowed1 % limit, can result in lower elongation values. Reductions ofas much as 15 % have been reported for a 1 % taper.

X1.4.6 Changes in the strain rate can affect the yieldstrength, tensile strength, and elongation values, especially formaterials which are highly strain rate sensitive. In general, theyield strength and tensile strength will increase with increasingstrain rate, although the effect on tensile strength is generallyless pronounced. Elongation values generally decrease as thestrain rate increases.

X1.4.7 Brittle materials require careful specimenpreparation, high quality surface finishes, large fillets at theends of the gauge length, oversize threaded grip sections, andcannot tolerate punch or scribe marks as gauge length indica-tors.

X1.4.8 Flattening of tubular products to permit testing doesalter the material properties, generally nonuniformly, in theflattened region which may affect test results.

X1.5 Measurement errors that can affect test results include:verification of the test force, extensometers, micrometers,

dividers, and other measurement devices, alignment and zero-ing of chart recording devices, and so forth.

X1.5.1 Measurement of the dimensions of as-cast, as-rolled,as-forged, and other test specimens with non-machined sur-faces may be imprecise due to the irregularity of the surfaceflatness.

X1.5.2 Materials with anisotropic flow characteristics mayexhibit non-circular cross sections after fracture and measure-ment precision may be affected, as a result (see Note 41).

X1.5.3 The corners of rectangular test specimens are subjectto constraint during deformation and the originally flat surfacesmay be parabolic in shape after testing which will affect theprecision of final cross-sectional area measurements (see Note46).

X1.5.4 If any portion of the fracture occurs outside of themiddle of the gauge length, or in a punch or scribe mark withinthe gauge length, the elongation and reduction of area valuesmay not be representative of the material. Wire specimens thatbreak at or within the grips may not produce test resultsrepresentative of the material.

X1.5.5 Use of specimens with shouldered ends (“button-head” tensiles) will produce lower 0.02 % offset yield strengthvalues than threaded specimens.

X1.6 Because standard reference materials with certifiedtensile property values are not available, it is not possible torigorously define the bias of tension tests. However, by the useof carefully designed and controlled interlaboratory studies, areasonable definition of the precision of tension test results canbe obtained.

X1.6.1 An interlaboratory test program3 was conducted inwhich six specimens each, of six different materials wereprepared and tested by each of six different laboratories. TablesX1.1-X1.6 present the precision statistics, as defined in Prac-tice E691, for: tensile strength, 0.02 % yield strength, 0.2 %yield strength, % elongation in 4D, % elongation in 5D, and% reduction in area. In each table, the first column lists the sixmaterials tested, the second column lists the average of theaverage results obtained by the laboratories, the third and fifthcolumns list the repeatability and reproducibility standarddeviations, the fourth and sixth columns list the coefficients ofvariation for these standard deviations, and the seventh andeighth columns list the 95 % repeatability and reproducibilitylimits.

X1.6.2 The averages (below columns four and six in eachtable) of the coefficients of variation permit a relative compari-son of the repeatability (within-laboratory precision) andreproducibility (between-laboratory precision) of the tensiontest parameters. This shows that the ductility measurementsexhibit less repeatability and reproducibility than the strengthmeasurements. The overall ranking from the least to the mostrepeatable and reproducible is: % elongation in 4D, % elonga-tion in 5D, % reduction in area, 0.02 % offset yield strength,0.2 % offset yield strength, and tensile strength. Note that therankings are in the same order for the repeatability andreproducibility average coefficients of variation and that the

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

reproducibility (between-laboratory precision) is poorer thanthe repeatability (within-laboratory precision) as would beexpected.

X1.6.3 No comments about bias can be made for theinterlaboratory study due to the lack of certified test results forthese specimens. However, examination of the test results

showed that one laboratory consistently exhibited higher thanaverage strength values and lower than average ductility valuesfor most of the specimens. One other laboratory had consis-tently lower than average tensile strength results for allspecimens.

TABLE X1.1 Precision Statistics—Tensile Strength, MPa [ksi]

NOTE 1—X is the average of the cell averages, that is, the grand mean for the test parameter,sr is the repeatability standard deviation (within-laboratory precision) in MPa [ksi],sr/ X is the coefficient of variation in %,sR is the reproducibility standard deviation (between-laboratory precision) in MPa [ksi],sR/ X is the coefficient of variation, %,r is the 95 % repeatability limits in MPa [ksi],R is the 95 % reproducibility limits in MPa [ksi].

Material X sr sr /X, % sR sR /X, % r R

EC-H19 176.9 [25.66] 4.3 [0.63] 2.45 4.3 [0.63] 2.45 12.1 [1.76] 12.1 [1.76]2024-T351 491.3 [71.26] 6.1 [0.88] 1.24 6.6 [0.96] 1.34 17.0 [2.47] 18.5 [2.68]

ASTM A105 596.9 [86.57] 4.1 [0.60] 0.69 8.7 [1.27] 1.47 11.6 [1.68] 24.5 [3.55]AISI 316 694.6 [100.75] 2.7 [0.39] 0.39 8.4 [1.22] 1.21 7.5 [1.09] 23.4 [3.39]

Inconel 600 685.9 [99.48] 2.9 [0.42] 0.43 5.0 [0.72] 0.72 8.2 [1.19] 13.9 [2.02]SAE 51410 1253.0 [181.73] 0.25 [0.46] 0.25 7.9 [1.14] 0.63 8.9 [1.29] 22.1 [ 3.20]

Averages: 0.91 1.30

TABLE X1.2 Precision Statistics—0.02 % Yield Strength, MPa [ksi]


EC-H19 111.4 [16.16] 4.5 [0.65] 4.00 8.2 [1.19] 7.37 12.5 [1.81] 23.0 [3.33]2024-T351 354.2 [51.38] 5.8 [0.84] 1.64 6.1 [0.89] 1.73 16.3 [2.36] 17.2 [2.49]

ASTM A105 411.1 [59.66] 8.3 [1.20] 2.02 13.1 [1.90] 3.18 23.2 [3.37] 36.6 [5.31]AISI 316 336.1 [48.75] 16.7 [2.42] 4.97 31.9 [4.63] 9.49 46.1 [6.68] 89.0 [12.91]

Inconel 600 267.1 [38.74] 3.2 [0.46] 1.18 5.2 [0.76] 1.96 8.8 [1.28] 14.7 [2.13]SAE 51410 723.2 [104.90] 16.6 [2.40] 2.29 21.9 [3.17] 3.02 46.4 [6.73] 61.2 [8.88]

Averages: 2.68 4.46

TABLE X1.3 Precision Statistics—0.2 % Yield Strength, MPa [ksi]


EC-H19 158.4 [22.98] 3.3 [0.47] 2.06 3.3 [0.48] 2.07 9.2 [1.33] 9.2 [1.33]2024-T351 362.9 [52.64] 5.1 [0.74] 1.41 5.4 [0.79] 1.49 14.3 [2.08] 15.2 [2.20]

ASTM A105 402.4 [58.36] 5.7 [0.83] 1.42 9.9 [1.44] 2.47 15.9 [2.31] 27.8 [4.03]AISI 316 481.1 [69.78] 6.6 [0.95] 1.36 19.5 [2.83] 4.06 18.1 [2.63] 54.7 [7.93]

Inconel 600 268.3 [38.91] 2.5 [0.36] 0.93 5.8 [0.85] 2.17 7.0 [1.01] 16.3 [2.37]SAE 51410 967.5 [140.33] 8.9 [1.29] 0.92 15.9 [2.30] 1.64 24.8 [3.60] 44.5 [6.45]

Averages: 1.35 2.32

TABLE X1.4 Precision Statistics—% Elongation in 4D for E8 Specimens

NOTE 1—Length of reduced section = 6D.

Material X sr sr/X, % sR sR/X, % r R

EC-H19 17.42 0.64 3.69 0.92 5.30 1.80 2.592024-T351 19.76 0.58 2.94 1.58 7.99 1.65 4.43

ASTM A105 29.10 0.76 2.62 0.98 3.38 2.13 2.76AISI 316 40.07 1.10 2.75 2.14 5.35 3.09 6.00

Inconel 600 44.28 0.66 1.50 1.54 3.48 1.86 4.31SAE 51410 14.48 0.48 3.29 0.99 6.83 1.34 2.77

Averages: 2.80 5.39

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

X2. MEASUREMENT OF SPECIMEN DIMENSIONS

X2.1 Measurement of specimen dimensions is critical intension testing, and it becomes more critical with decreasingspecimen size, as a given absolute error becomes a largerrelative (percent) error. Measuring devices and proceduresshould be selected carefully, so as to minimize measurementerror and provide good repeatability and reproducibility.

X2.2 Relative measurement error should be kept at or below1 %, where possible. Ideally, this 1 % error should include notonly the resolution of the measuring device but also thevariability commonly referred to as repeatability and reproduc-ibility. (Repeatability is the ability of any operator to obtainsimilar measurements in repeated trials. Reproducibility is theability of multiple operators to obtain similar measurements.)

X2.3 Formal evaluation of gage repeatability and reproduc-ibility (GR and R) by way of a GR and R study is highlyrecommended. A GR and R study involves having multipleoperators each take two or three measurements of a number ofparts—in this case, test specimens. Analysis, usually done bycomputer, involves comparing the observed measurementvariations to a tolerance the procedure is to determine confor-mance to. High GR and R percentages (more than 20 %)indicate much variability relative to the tolerance, whereas lowpercentages (10 % or lower) indicate the opposite. The analysisalso estimates, independently, the repeatability and reproduc-ibility.

X2.4 GR and R studies in which nontechnical personnelused different brands and models of hand-held micrometershave given results varying from about 10 % (excellent) tonearly 100 % (essentially useless), relative to a dimensionaltolerance of 0.075 mm [0.003 in.]. The user is thereforeadvised to be very careful in selecting devices, setting up

measurement procedures, and training personnel.

X2.5 With a 0.075 mm [0.003 in.] tolerance, a 10 % GR andR result (exceptionally good, even for digital hand-held mi-crometers reading to 0.001 mm [0.00005 in.]) indicates that thetotal variation due to repeatability and reproducibility is around0.0075 [0.0003 in.]. This is less than or equal to 1 % only if alldimensions to be measured are greater than or equal to 0.75mm [0.03 in.]. The relative error in using this device tomeasure thickness of a 0.25 mm [0.01 in.] flat tensile specimenwould be 3 %—which is considerably more than that allowedfor force or strain measurement.

X2.6 Dimensional measurement errors can be identified asthe cause of many out-of-control signals, as indicated bystatistical process control (SPC) charts used to monitor tensiontesting procedures. This has been the experience of a produc-tion laboratory employing SPC methodology and the besthand-held micrometers available (from a GR and R standpoint)in testing of 0.45 to 6.35 mm [0.018 to 0.25 in.] flat rolled steelproducts.

X2.7 Factors which affect GR and R, sometimesdramatically, and which should be considered in the selectionand evaluation of hardware and procedures include:

X2.7.1 Resolution,

X2.7.2 Verification,

X2.7.3 Zeroing,

X2.7.4 Type of anvil (flat, rounded, or pointed),

X2.7.5 Cleanliness of part and anvil surfaces,

X2.7.6 User-friendliness of measuring device,

TABLE X1.5 Precision Statistics—% Elongation in 5D for E8M Specimens

NOTE 1—Length of reduced section = 6D.


EC-H19 14.60 0.59 4.07 0.66 4.54 1.65 1.852024-T351 17.99 0.63 3.48 1.71 9.51 1.81 4.81

ASTM A105 25.63 0.77 2.99 1.30 5.06 2.15 3.63AISI 316 35.93 0.71 1.98 2.68 7.45 2.00 7.49

Inconel 600 41.58 0.67 1.61 1.60 3.86 1.88 4.49SAE 51410 13.39 0.45 3.61 0.96 7.75 1.25 2.89

Averages: 2.96 6.36

TABLE X1.6 Precision Statistics—% Reduction in Area


EC-H19 79.15 1.93 2.43 2.01 2.54 5.44 5.672024-T351 30.41 2.09 6.87 3.59 11.79 5.79 10.01

ASTM A105 65.59 0.84 1.28 1.26 1.92 2.35 3.53AISI 316 71.49 0.99 1.39 1.60 2.25 2.78 4.50

Inconel 600 59.34 0.67 1.14 0.70 1.18 1.89 1.97SAE 51410 50.49 1.86 3.69 3.95 7.81 5.21 11.05

Averages: 2.80 4.58

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

X2.7.7 Stability/temperature variations,

X2.7.8 Coating removal,

X2.7.9 Operator technique, and

X2.7.10 Ratchets or other features used to regulate theclamping force.

X2.8 Flat anvils are generally preferred for measuring thedimensions of round or flat specimens which have relativelysmooth surfaces. One exception is that rounded or pointedanvils must be used in measuring the thickness of curvedspecimens taken from large-diameter tubing (see Fig. 13), toprevent overstating the thickness. (Another concern for thesecurved specimens is the error that can be introduced throughuse of the equation A = W×T; see 7.2.3.)

X2.9 Heavy coatings should generally be removed from atleast one grip end of flat specimens taken from coated productsto permit accurate measurement of base metal thickness,assuming (a) the base metal properties are what are desired, (b)the coating does not contribute significantly to the strength ofthe product, and (c) coating removal can be easily accom-plished (some coatings may be easily removed by chemical

stripping). Otherwise, it may be advisable to leave the coatingintact and determine the base metal thickness by an alternatemethod. Where this issue may arise, all parties involved incomparison or conformance testing should agree as to whetheror not coatings are to be removed before measurement.

X2.10 As an example of how the considerations identifiedabove affect dimensional measurement procedures, considerthe case of measuring the thickness of 0.40 mm [0.015 in.)painted, flat rolled steel specimens. The paint should beremoved prior to measurement, if possible. The measurementdevice used should have flat anvils, must read to 0.0025 mm[0.0001 in.] or better, and must have excellent repeatability andreproducibility. Since GR and R is a significant concern, it willbe best to use a device which has a feature for regulating theclamping force used, and devices without digital displaysshould be avoided to prevent reading errors. Before use of thedevice, and periodically during use, the anvils should becleaned, and the device should be verified or zeroed (if anelectronic display is used) or both. Finally, personnel should betrained and audited periodically to ensure that the measuringdevice is being used correctly and consistently by all.

X3. SUGGESTED ACCREDITATION CRITERIA FOR LABORATORIES PERFORMING TENSILE TESTS

X3.1 Scope

X3.1.1 The following are specific features that an assessormay check to assess a laboratory’s technical competence, if thelaboratory is performing tests in accordance with Test MethodsE8/E8M.

X3.2 Preparation

X3.2.1 The laboratory should follow documented proce-dures to ensure that machining or other preparation generatesspecimens conforming to applicable tolerances and require-ments of Test Methods E8/E8M. Particularly important arethose requirements that pertain to the dimensions and finish ofreduced sections, as found in the text and in applicable figures.

X3.2.2 Where gauge marks are used, the laboratory shouldemploy documented gauge marking procedures to ensure thatthe marks and gauge lengths comply with the tolerances andguidelines of Test Methods E8/E8M.

X3.2.2.1 The gauge marking procedure used should notdeleteriously affect the test results.

NOTE X3.1—Frequent occurrence of fracturing at the gauge marks mayindicate that gage marks have excessive depth or sharpness and may beaffecting test results.

X3.3 Test Equipment

X3.3.1 As specified in the Apparatus sections of TestMethods E8/E8M, the axis of the test specimen should coin-cide with the center line of the heads of the testing machine, inorder to minimize bending stresses which could affect theresults.

X3.3.2 Equipment verification requirements of Practices E4and E83 shall be met. Documentation showing the verificationwork to have been thorough and technically correct should beavailable.

X3.3.2.1 Verification reports shall demonstrate that forceand extension readings have been taken at the prescribedintervals and that the prescribed runs have been completed.

X3.3.3 Extensometers used shall meet all requirements ofTest Methods E8/E8M as to the classification of device to beused for the results determined. For example, an extensometernot meeting the Class B2 requirements of Practice E83 may notbe used in determination of offset yield strengths.

X3.3.4 Before computerized or automated test equipment isput into routine service, or following a software revision, it isrecommended that measures be taken to verify proper opera-tion and result interpretation. Guide E1856 addresses thisconcern.

X3.3.5 Micrometers and other devices used in measurementof specimen dimensions should be selected, maintained andused in such a manner as to comply with the appendixes of TestMethods E8/E8M on measurement. Traceability to nationalstandards should be established for these devices, and reason-able effort should be employed to prevent errors greater than1 % from being generated as a result of measurement error,resolution, and rounding practice.

X3.4 Procedures

X3.4.1 The test machine shall be set up and zeroed in sucha manner that zero force indication signifies a state of zeroforce on the specimen, as indicated in the Zeroing of the TestMachine sections of Test Methods E8/E8M.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

NOTE X3.2—Provisions should be made to ensure that zero readings areproperly maintained, from test to test. These may include, for example,zeroing after a predetermined number of tests or each time, under zeroforce conditions, the indicator exceeds a predetermined value.

X3.4.2 Upon request, the laboratory should be capable ofdemonstrating (perhaps through time, force, displacement orextensometer measurements, or both) that the test speeds usedconform to the requirements of Test Methods E8/E8M, or otherstandards which take precedence.

X3.4.3 Upon request, the laboratory should be capable ofdemonstrating that the offsets and extensions used in determin-ing yield strengths conform to the requirements of TestMethods E8/E8M and are constructed so as to indicate theforces corresponding to the desired offset strain or total strain.

NOTE X3.3—Use caution when performing calculations with extensom-eter magnification, because the manufacturer may report strainmagnification, which relates the strain (not the elongation) to the x-axisdisplacement on the stress strain diagram. A user or assessor interested inan extensometer’s magnification may use calibration equipment to deter-mine the ratio between elongation and chart travel or may verify areported magnification by calculating the Young’s modulus from tests ofspecimens of a known nominal modulus.

X3.4.4 Measurement of elongation shall conform to re-quirements of Test Methods E8/E8M.

NOTE X3.4—Test Methods E8/E8M permit the measurement andreporting of elongation at fracture in place of elongation, as is often donein automated testing.

X3.4.5 Reduction of area, when required, shall be deter-mined in accordance with the requirements of Test MethodsE8/E8M.

X3.4.6 Procedures for recording, calculating, and reportingdata and test results shall conform to all applicable require-ments of Test Methods E8/E8M. In addition, whereverpractical, the procedures should also be in accordance withwidely accepted provisions of good laboratory practice, such asthose detailed below.

X3.4.6.1 When recording data, personnel should record allfigures that are definite, plus the best estimate of the first figurewhich is uncertain. (If a result is known to be approximatelymidway between 26 and 27, 26.5 should be the result recorded(not 26, 27, or 26.475).

X3.4.6.2 When performing calculations, personnel shouldavoid compounding of rounding errors. This may be accom-plished by performing one large calculation, rather than severalcalculations using individual results. Alternatively, if multi-step calculations are done, intermediate results should not berounded before use in subsequent calculations.

X3.4.6.3 In rounding, no final result should retain moresignificant figures than the least-significant-figure measure-ment or data point used in the calculation.

X3.5 Retention

X3.5.1 A retention program appropriate for the nature andfrequency of testing done in the laboratory should be main-tained. Items that may warrant retention for defined timeperiods include:

X3.5.1.1 Raw data and forms,

X3.5.1.2 Force-elongation or stress-strain charts,

X3.5.1.3 Computer printouts of curves and test results,

X3.5.1.4 Data and results stored on computer discs or harddrives,

X3.5.1.5 Broken specimens,

X3.5.1.6 Excess material,

X3.5.1.7 Test reports, and

X3.5.1.8 Verification reports and certifications.

X3.6 Environment

X3.6.1 All test equipment should be located and connectedto power sources in such a manner as to minimize the effectsof vibrations and electrical disturbances on raw data collected,stress-strain charts, and operation of equipment.

X3.7 Controls

X3.7.1 Controlled procedures and work instructions shouldcover all aspects of specimen preparation, tensile testing, andresult reporting. These documents should be readily availableto all involved in the documented tasks.

X3.7.2 Clear, concise, operating instructions should bemaintained for equipment used in specimen preparation andtensile testing. These instructions should be readily available toall qualified operators.

X3.7.3 All applicable verification requirements shall bemet, as detailed in X3.3.2.

X3.7.4 It is recommended that special studies and programsbe employed to monitor and control tensile testing, becausetensile test results are easily affected by operators, measuringdevices, and test equipment. Examples of such programsinclude but are not limited to:

X3.7.4.1 Round-robin studies, proficiency tests, or othercross-checks,

X3.7.4.2 Repeatability and reproducibility (R and R)studies,

X3.7.4.3 Control charting, andX3.7.4.4 Determination of typical lab uncertainties for each

result typically reported.

NOTE X3.5—For nondestructive testing, repeatability and reproducibil-ity are often measured by conducting gage R and R studies, as discussedin Appendix X2 of Test Methods E8/E8M. These studies involve repeateddetermination of a test result, using a single part or specimen, so gage Rand Rs are not directly applicable to mechanical properties, which areobtained through destructive testing. (True differences between even thebest duplicate specimens manifest themselves in the form of poorer R andR results than would be obtained for perfect duplicates.) Nevertheless,quasi-R and R studies conducted with these limitations taken intoconsideration may be helpful in analyzing sources of error and improvingreliability of test results.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

X4. ADDITIONAL INFORMATION ON SPEED OF TESTING AND EXAMPLES

X4.1 Many materials are strain-rate sensitive that is, theyield strength or tensile strength of the material is a function ofthe rate at which the material is being deformed. The yieldstrength of some materials can change by more than ten percentwhen tested with the slowest and then the highest speedspermitted by Test Methods E8/E8M. In order to reproduceyield test results, for strain-rate sensitive materials, it isimportant that strain rates during the determination of yield aresimilar.

X4.2 The following paragraphs further explain the variousControl Methods required to be used by Test Methods E8/E8Mwhen other guidance is not given. When other test speedrequirements are specified, those speeds must be followed tocomply with this test method. For example, aerospace specifi-cations often require a test speed when determining yieldstrength to be a strain rate equal to 0.005 6 0.002 mm/mm/min[in./in./min]; when specified, that speed must be followed inorder to comply with this standard.

X4.2.1 Control Method A - Rate of Stressing Method forDetermining Yield Properties – This method has been thedefault method of control in Test Methods E8/E8M for manyyears. In this method, the crosshead speed of the machine isadjusted during the linear elastic portion of the curve to achievethe desired stress rate (or the speed is set to a predeterminedvalue known to achieve the desired stress rate). The crossheadspeed is not adjusted when the material begins to yield. Theadvantage of this control method is that it does not require anytransducers other than the load indicator itself, although, loadpacers and stress-rate indicators can be helpful. This method ofcontrol has a limitation in that the strain rate of the specimenat yield depends on the slope of the stress-strain curve (tangentmodulus) and the testing machine stiffness. Because of this, thestrain rate of the specimen when yield is determined can bedifferent for different specimen sizes, different specimenconfigurations, different gripping configurations, and differenttesting machines. This difference in strain rate can affect thereproducibility of yield strength in strain-rate-sensitive mate-rials.

X4.2.1.1 It is not the intent of this method to run the testingmachine in closed-loop force control, because as the materialbegins to yield the testing machine will speed up, possibly toits maximum speed. However, using closed-loop force controlduring the elastic region of the test and switching to anequivalent crosshead speed prior to yield is an acceptablemethod.

X4.2.2 Control Method B —Rate of Straining ControlMethod for Determining Yield Properties - This method isusually performed with a testing machine that has a closed-loop control system that uses feedback from an extensometer to

automatically adjust the speed of the testing machine.However, some skilled operators can monitor a strain rateindicator attached to the extensometer and adjust the speed ofthe testing machine manually to maintain the required strainrate test speed. To maintain constant strain rate control duringa test, the crosshead speed of the testing machine must slowdown drastically when the specimen begins to yield. Thismethod has three advantages. (1) The time to achieve yieldresults is short (about 20 to 40 s). (2) The reproducibility ofyield strength test results from machine to machine andlaboratory to laboratory is good. (3) The agreement with theresults of Control Method C is good, because the strain ratesare similar when the specimen’s yield strength is determined.This method has three disadvantages. (1) The testing equip-ment is generally more expensive. (2) Proper control and safetydepend on the control parameters to be properly set and that theextensometer integrity be maintained (accidental slippage ofthe extensometer can result in unexpected movement of thecrosshead). Proper safety limits must be set to ensure safety ofpersonnel and equipment. (3) When materials have yield pointsor yield discontinuously, a machine under closed-loop strain-rate control can behave erratically. This control method is notrecommended for materials that yield discontinuously.

X4.2.3 Control Method C - Crosshead Speed ControlMethod for Determining Yield Properties—This method can beperformed on any testing machine that has reasonably goodcrosshead speed control. This method has three advantages. (1)The reproducibility from machine to machine and laboratory tolaboratory is good. (2) The agreement with Control Method Bis good, because the strain rates are similar when the speci-men’s yield strength is determined. (3) This method of con-trolling a testing machine is excellent for materials that yielddiscontinuously. The disadvantage of this method of control isthat the test time to yield can be more than three minutes,depending on the material being tested and the compliance ofthe testing machine including its grip assemblies.

X4.2.3.1 An example using SI metric units of how to applyControl Method C to testing Specimen 1 in Fig. 13 is asfollows. The length of the reduced section, that is, dimension Ain Fig. 13, is equal to 60 mm. The crosshead speed isdetermined per Control Method C by multiplying 60 mm by0.015 mm/mm/min to arrive at a crosshead speed of 0.9mm/min.

X4.2.3.2 An example using U.S. customary units of how toapply Control Method C to testing Specimen 1 in Fig. 13 is asfollows. The length of the reduced section, that is, dimension Ain Fig. 13 is equal to 2.25 in. The crosshead speed isdetermined per Control Method C by multiplying 2.25 in. by0.015 in./in./min to arrive at a crosshead speed of 0.034in./min.

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

SUMMARY OF CHANGES

Committee E28 has identified the location of selected changes to this standard since the last issue(E8/E8M-13) that may impact the use of this standard. (Approved July 1, 2013.)

(1) 3.1.4 was revised. (2) 3.1.5 was added.

Committee E28 has identified the location of selected changes to this standard since the last issue (E8/E8M-11)that may impact the use of this standard. (Approved June. 1, 2013.)

(1) Replaced 3.1.(2) Added 3.1.2.(3) Reformatted 3.1.3.(4) Reformatted 3.1.4.

(5) Added 3.1.7, 3.1.8, and 3.1.12.(6) Reformatted 3.1.11.(7) Added 3.2.1.(8) Added Note 32.

ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.

This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.

This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or [email protected] (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).

E8/E8M − 13a



--`````,`,,``,`,,,``,`,```,,,``-`-`,,`,,`,`,,`---

Standard Test Methods for Tension Testing of Metallic ... · PDF fileDesignation: E8/E8M...

Documents

Transcript of Standard Test Methods for Tension Testing of Metallic ... · PDF fileDesignation: E8/E8M...